After the death of the Most Noble Messenger, peace and blessings be upon him and his family, and the departure of that great leader from the midst of society, the interests of Islam and the ummah made it imperative that a distinguished and worthy leader, a being overflowing with knowledge and piety, should assume the governance of the newly emergent Islamic movement which needed continued instruction. This was necessary in order to guarantee the continuity of Islam, to safeguard it from deviation, to prevent the ummah from falling back into its former reprehensible social and moral habits, and to reinforce as much as possible the Islamic socio-political order.
To leave the question of leadership to a community that had only recently escaped the fetters of Jahiliyyah and from whose spirit and soul the traces of Jahili beliefs had not yet disappeared, would not have sufficed to secure the lofty aims of the Prophet or to protect the religion from the danger of negative forces.
The only path was then for a worthy personality, erudite in all matters concerning the message, equipped with intelligence and extensive religious knowledge, possessed of a luminous faith and exempt from error just like the founder of Islam, should gather the reins of affairs in his hands in order to pursue with care and subtlety the task of training and educating men and solve the problems and questions concerning the shari'ah that might arise during the period of his governance.
Historical evidence shows that the Messenger of God, on his return from the Farewell Pilgrimage, fulfilled this need on the eighteenth day of Dhu 'l-Hijjah by designating his legatee and successor in accordance with divine command, thus showing the people the path to be followed for the ummah to gain felicity.
In the tenth year of the Hijrah, which was also the last year in the life of the Beloved Prophet, peace and blessings be upon him and his family, he decided to participate in the great Islamic gathering that was to be held in Makkah. Once it became known that the Prophet was setting out for the Ka'bah, throngs of Muslims from near and far set out in the direction of Madinah in order to have the honor of travelling with him, to learn the pilgrimage rites from him, and to perform that great ritual of Islam directly in his presence.
Finally the great caravan set out, composed of the Migrants (muhajirun), the Helpers (ansar), and the other Muslims who were leaving Madinah in the company of their leader, and they advanced towards Makkah. After entering the city, they began their acts of worship at the Ka'bah. During those days the city of Makkah witnessed one of the most glorious of Islamic ceremonies, performed by thousands of Muslims who were gathered around their leader like the thunderous waves of an ocean. The Prophet too was proud in front of his Lord that on such a day he was able to see the results of his unremitting efforts and toil.
After that year's pilgrimage had been completed - the pilgrimage known as the Farewell Pilgrimage - the Prophet left the House of God together with the great crowd of pilgrims (hujjaj), estimated by historians to have numbered between ninety and one hundred and twenty thousand, and prepared to return to Madinah. The caravan traversed several valleys and arrived at a waterless plain known as Ghadir Khumm.  It was then that the messenger of revelation came to the Prophet and ordered him to halt. The Prophet stopped the caravan and waited for the stragglers to catch up with the main body.
This sudden halt in that torrid landscape beneath the burning midday sun astonished the weary travellers, but it was not long before Jibril (Gabriel) the trustworthy angel of revelation conveyed to the pure soul of the Prophet a heavenly message the categorical and clear command of the Creator that he should appoint and announce his legatee and successor:
O Messenger of God, convey to mankind the command that God has sent you. If you do not do so, you will not have conveyed the prophetic message. God will protect you from the harm men might cause you.(5:67)
Close attention to the content of this verse demonstrates to us the important truth that the proclamation of this particular divine message was of such importance and gravity that if the Prophet were to shrink from conveying it, it would be equivalent to his refraining from fulfilling his entire prophetic mission, while conveying it to the ummah was tantamount to the completion of that mission.
In the verse, the Most Noble Prophet, peace and blessings be upon him and his family, is reminded of the extraordinary significance of the task that has been assigned to him, and he is guaranteed protection from any dangers that might result from proclaiming the message.
At the same time, not more than a few days were left in the glorious life of the Prophet, peace and blessings be upon him and his family, for he died seventy days after the event of Ghadir Khumm. All that he had achieved in the course of twenty three years since the beginning of revelation, all that man needed for his guidance and felicity, was now at the disposal of mankind. Only one particular matter remained, the proclamation of which would complete his prophetic mission and bring his task to complete fruition.
It was in addition probable that while fulfilling the instructions he had received the Prophet would be attacked or harmed by evil wishers, and in order to reinforce his determination God informed him that He would protect him and guard him against being harmed.
The content of those instructions must have been particularly sensitive in order for their fulfillment to have been coterminous with the entirety of the Prophet's mission and for the failure to proclaim them to have damaged and diminish prophethood itself. Moreover, the Arab mentality prevailing at the time tended to regard the aged persons of each tribe as best suited for positions of leadership and not to consider younger persons as qualified; this feature hardly constituted a favorable climate for the proclamation of God's command.
The spirit of the Prophet was also troubled and surely pained by certain bitter memories. He had not yet forgotten the negative attitude of certain narrow minded people to the appointment of Usamah and Attab b. Usayb as commanders, for when he appointed the former as commander of the army and the latter as commander of Makkah, some of the Companions raised their voices in protest.
All of these constituted factors that made the declaration of 'Ali b. Abi Talib, peace be upon him, someone as young as thirty three years of age, a formidable and even intimidating task for the Prophet.
In addition, many of those who had now joined the ranks of the Muslims and entered the circle of the Prophet's Companions, had earlier fought against 'Ali, peace be upon him, which further increased the delicacy of the situation; their hearts were troubled by the memory of those events and fanned the flames of hatred within them.
Despite all those unfavorable circumstances, the divine will decreed that the best and most exalted personage who through the grace of God had attained the highest spiritual station next to the Prophet should be appointed as his successor, so that by the designation of this great man to lead the ummah, the universal message of the Prophet should be completed.
According not only to Shi'i scholars of hadith but also certain Sunni scholars as well,  the Qur'anic verse in question was revealed on the day of Ghadir Khumm, the day on which the Prophet, the veracity of whose speech is guaranteed by God Himself, received the divine command, by way of revelation and in accordance with wisdom, to expound the last and most essential foundation of Islam by presenting 'Ali, peace be upon him, to the people as his successor.
Yes, that personage whose being had never been polluted by polytheism or sin, whose entire life had been devoted to disseminating the teachings of religion and promoting Islam, who was a complete reflection of the Messenger of God he was the one fitted to preserve the laws and norms of religion, to assume the leadership of humanity as it advanced toward perfection and salvation. It was his form alone that was worthy of putting on the garb of Imamate and leadership.
The time for the noon prayer arrived, and the great throng that had descended at Ghadir Khumm performed the prayer behind the Prophet.  Then the Prophet advanced to the middle of the crowd that filled the whole plain in anticipation of an historic event, in order to implement the categorical command of God. He mounted a pulpit that had been improvised from camel litters, in order for everyone to be able to see and to hear him.
He then began to deliver his address, in powerful, clear and compelling tones, so that everyone was able to hear him or at least be aware of what was transpiring.
After praising and thanking God, to whom alone belong absolute power, wisdom and vision, and whose governance, knowledge and perception are immune to defect and decline, he said:
"O people, I will soon be responding to the call of my Lord and departing from your midst. I will be held to account, as you too will be. Will you not bear witness that there is none worthy of worship other than God, the One and Unique? Do you not testify that Muhammad is His servant and messenger? Are not paradise, hellfire and death all realities? Is it not true the day of requital and resurrection will definitely come, and that God will restore to life those who lie buried in the ground?"
The voice of the multitude arose in response: "Indeed we bear witness to all of that."
Then he continued: "Now that the Day of Requital lies before us, and you believe in the raising of the dead on the Plain of Resurrection and that you will enter the presence of your prophet on that day, pay heed to the manner in which you treat the two weighty (thaqalayn) and precious legacies I leave you as I depart for the hereafter. 
"That which is the greater of the two is the Book of God. It is in your hands as well as His, so lay hold of it firmly lest you fall into misguidance. The lesser of the two legacies is my progeny and the people of my household. God has informed me that my two legacies shall never be separated from each other until the Day of Resurrection.
"O people, do not turn away from these two legacies. As long as you have recourse to them, you will never go astray the Book of God and my family." 
At this point, the Prophet, peace and blessings be upon him and his family, called 'Ali, peace be upon him, to his side. He took hold of his hand and raised it up high, thereby presenting him with all his qualities and attributes to the gathered throng. Then the Messenger of God asked: "O people, who is more deserving of the believers than their own persons?" They answered: "God and His Messenger know better." He continued: "For whomsoever I was his master 'Ali is now his master." 
After completing his speech, the Prophet requested the people to convey what he had said to those who were absent.
The one who was thus installed in the seat of Islamic leadership on that day, in accordance with divine command and by virtue of the Prophet's declaration, who was entrusted with the guidance of the ummah, was 'Ali. The most worthy and renowned man in the Islamic community, he who was a treasury of knowledge and an incarnation of virtue, had been selected as the leader of the Muslims, and by proclaiming the important matter of Imamate and caliphate the Prophet had given a decisive and binding command to the ummah.
The assembled multitude had not begun to disperse when the agent of revelation revealed this verse to the Prophet:
Today I have perfected for you your religion, completed for you My bounty, and chosen Islam for you as religion. (5:3) 
According to al-Ya'qubi, "This verse, revealed at Ghadir Khumm, was the last verse to be revealed to the Most Noble Messenger, peace and blessings be upon him and his family." 
The Prophet left the place where he was standing, while all around the sound of takbir was to be heard as the pilgrims expressed their warm and enthusiastic feelings towards 'Ali, peace be upon him. People came up to him in groups and congratulated him on his appointment as leader, addressing him as their master and the master of every believer, man and woman.
The well known poet Hassan b. Thabit who was present on that occasion, composed and recited to the people, with the permission of the Prophet, an eloquent ode in honor of the auspicious event.
The verse just cited, which declares how God has on this day perfected His religion and completed His blessing, permits us to understand the full significance of what had transpired. A momentous happening must have occurred for the Qur'an to qualify it in such terms, for the Islam that God has chosen and approved was the Islam of that day. the religion of truth had attained its perfection through the appointment of 'Ali, peace be upon him, and God's blessing to mankind had been completed through his selection as the legatee (wasiyy) of the Prophet, peace and blessings be upon him and his family.
Both universally accepted hadith and reliable books of history to which Shi'is and Sunnis alike refer emphasize that this verse was revealed at Ghadir Khumm on the day that the Prophet, peace and blessings be upon him and his family, had entrusted 'Ali, peace be upon him, with the responsibility of governing and leading the ummah after himself. Surah al-Ma'idah, to the early part of which this verse belongs, is the last surah to have been revealed to the Most Noble Messenger, peace and blessings be upon him and his family, in the unanimous view of the exegetes. This means that its revelation took during the last days of his blessed life, and no further command was revealed to him thereafter by his Lord.
The view held by some that the verse refers to the beginning of his prophetic mission, meaning that it was on that day that God's religion was perfected and His blessing completed, is baseless, and utterly incompatible both with the historical facts and the correct interpretation of the verse. The day on which the mission of the Prophet began was the beginning of the divine blessing, not its culmination, an extremely important difference. What is at issue in the verse is the completion of the blessing and the perfection of religion; now that this matter has been accomplished, Islam is chosen and approved as religion for mankind. Neither history nor hadith can support the opposing view.
The momentous scene that Ghadir Khumm witnessed and the task that the Prophet, peace and blessings be upon him and his family, fulfilled on that day had long lasting consequences for the history of Islam. Apart from those who are prisoners to fanaticism and mental stagnation, no historian who is concerned with the recording of events and the preservation of historical fact can ignore what took place on that day or conceal the matters that are connected with it. During the early centuries of Islamic history, the day of Ghadir Khumm was well known and accepted as an auspicious occasion, and there are many indications that all Muslims participated in celebrating it.
Thus the well known historian Ibn Khallikan describes the eighteenth of Dhu 'l-Hijjah as the Day of Ghadir Khumm,  and al-Mas'udi mentions the night of the same day as the night of the festival of Ghadir Khumm.  Abu Rayhan al-Biruni, the famous Iranian scholar of the fifth century, includes the festival of Ghadir Khumm among the festivals that the Muslims celebrated in his time. In his Matalib al-Su'ul, the Shafi'i scholar Ibn Talhah writes: "The day of Ghadir Khumm is a festive day and an historic occasion, for it was then that the Messenger of God, peace and blessings be upon him and his family, clearly and explicitly nominated 'Ali, peace be upon him, as Imam and leader of the Muslims after him." 
Now let us see what the Messenger of God meant by the word "master" (mawla) when he said: "For whomsoever I was his master, 'Ali is now his master." Does it mean one who has prior rights of disposition, as the concomitant of the absolute governance of one person over another, or simply a helper and friend?
By referring to the Qur'an we can see that the first meaning is the correct one, for God says of the Prophet: "The Prophet has a greater claim to the souls of the believers than the believers themselves."(33:6) In addition, there are many places in the Qur'an where the word mawla occurs with the meaning of wali or ruler. 
The one who has a greater claim on the souls of others than they do themselves must have a priori a similar claim to their property, and will therefore necessarily have the right of absolute governance over them, a governance that permits no disobedience to his orders and commands.
The rank that this implies was first granted by God to His Prophet; it was God who endowed him with authority over the lives and property of the believers and gave him prior rights of disposition in every respect.
There are numerous indications and proofs that the meaning of wali in the traditions relating to Ghadir Khumm is identical to awla ("has a greater claim") in the verse we have just cited. Just as the Messenger of God, peace and blessings be upon him and his family, enjoyed absolute governance based on the Qur'an, so too did the Commander of the Faithful, 'Ali, peace be upon him, have the same rank and attribute, the only difference being that with the sealing of prophethood with the termination of the Prophet's mission, the gate of prophethood was closed. With this single exception, all the offices of the Prophet were transferred to 'Ali.
The first citation that clarifies the meaning of wali in the hadith is a sentence uttered by the Prophet, peace and blessings be upon him and his family, before he proclaimed 'Ali, peace be upon him, to be his successor. He asked: "Do I not have greater claims on you than your own selves?"
Here, while proclaiming his own authority over the Muslims, after obtaining their assent to the fact that he had greater claims on them than their own selves, he added: "For whomsoever I was his master, 'Ali is his master." The meaning of 'Ali, peace be upon him, being master must necessarily include the sense of awla ("having greater claims"), the same station that the Prophet himself had with respect to the believers. If the Prophet, peace and blessings be upon him and his family, had intended something else, there would have been no reason for him first to gain assent to his own possession of "greater claims". Could the meaning of mawla possibly be a simple friendship that exists among Muslims?
At the beginning of his address to the people, the Prophet, peace and blessings be upon him and his family, said: "Do you bear witness that there is none worthy of worship other than God, the One and unique, and do you believe that Muhammad is His servant and messenger and that paradise and hellfire are both realities?"
Could the reason for posing these questions have anything other than preparing the people to accept a principle comparable to those contained in the questions? Was it not the purpose of the Messenger of God, peace and blessings be upon him and his family, to make the people understand that acceptance of the caliphate and successorship of 'Ali, peace be upon him, which he was about to announce was on the same level as those three principles divine unity, prophethood, and resurrection?
If what the Prophet, peace and blessings be upon him and his family, meant by mawla nothing more than friend and protector, friendship with 'Ali would have been exactly the same as any other friendship prevailing among the believers since the very beginning of Islam as part of Islamic brotherhood. would have been no need to proclaim it in such a vast gathering, preceded by all kinds of detailed prefatory remarks and gaining the assent of the people to the three basic principles.
Furthermore, the Prophet, peace and blessings be upon him and mentioned his own death before presenting 'Ali, peace be upon him, to that great assembly he informed those present that he would soon be quitting this transitory realm. By making this statement, he wished in reality to fill the vacuum of leadership that would arise after him by appointing 'Ali, peace be upon him, as his successor. Mere friendship and love for 'Ali be upon him, could not alone have played a crucial role in Islamic society. Would it have been in any way necessary for the Prophet, peace and blessings be upon him and his family, to deliver a lengthy speech under the burning sun to an assembly of one hundred thousand people simply to expound love for 'Ali, be u him? Had not the Qur'an already proclaimed the believers to be friends and brothers to each other?
In view of all these consideration, it is not rationally acceptable that the Prophet, peace and blessings be upon him and his family, should on that occasion have been speaking of love for 'Ali, peace be upon him.
Moreover, after the Prophet, peace and blessings be upon him and his family, had finished speaking, a large number of the Companions came up to 'Ali, peace be upon him, and offered him their felicitations in a stream that continued until it was time for the sunset prayer. Abu Bakr, 'Uthman, Talhah and al-Zubayr were among those who offered 'Ali, peace be upon him, their on being appointed successor. 'Umar was among the first to address 'Ali, saying: "Well done, son of Abu Talib! Congratulation on this appointment; you have become the master of every believer, man and woman alike." 
Had 'Ali, peace be upon him, gained any other appointment at that time which might have qualified him for these congratulations? Was not 'Ali, peace be upon him, known until that point as an ordinary Muslim deserving of friendship like any other?
Hassan b. Thabit, the celebrated poet of the Prophet, peace and blessings be upon him and his family, was present among the pilgrims, and he understood the word mawla to imply the Imamate and leadership, He said in one of his poems: "The Prophet turned to the people and said to 'Ali 'Arise! I make you henceforth the leader and guide of the people.'"
If one studies the whole of the Prophet's speech with an open mind, free of prejudice and preconceived notions, and examines the evidence and indications it contains, he cannot fail to derive but a single meaning from the word mawla as applied to 'Ali b. Abi Talib, peace be upon him: the one who has prior rights of disposition and the right of absolute governance.
If the Prophet, peace and blessings be upon him and his family, did not use the word "ruler" at Ghadir Khumm when referring to 'Ali, peace be upon him, saying, for example, "after me 'Ali will be your ruler," it is because he generally used the word amir (commander) in the context of military affairs and the organization of the pilgrimage, whereas the word wilayah (authority or governance) was used in connection with the affairs of the ummah and indeed he referred to himself as the wali of the believers. Not even God referred to the prophet, peace and blessings be upon him and his family, as a ruler in the Qur'an, nor did the Prophet ever call himself a ruler or commander in any hadith. In fact the Qur'an says explicitly. "It is God and His Messenger alone who are your wali, and those who establish prayers and regular charity and bow down humbly in worship."(5:56) 
In reality, the link between the Prophet, peace and blessings be upon him and his family, to whom is entrusted the supervision of the Muslims, and the Islamic ummah is like the relationship of a father with his offspring, for he is responsible for administering their affairs and protecting their interest; it is not a relationship of ruler and ruled.
Likewise, the Prophet, peace and blessings be upon him and his family, did not use the word caliph or successor with respect to 'Ali, peace be upon him, because obedience to a successor becomes incumbent only after the death of the one to whose authority he succeeds, whereas the intention of the Prophet, peace and blessings be upon him and his family, was the obedience to 'Ali, peace be upon him, was obligatory for the Muslims even before he died. He therefore called him the master of the believers, implying his possession of authority both before and after the death of the Most Noble Messenger, peace and blessings be upon him and his family. Based on the hadith of Ghadir Khumm, he was the master of the Muslims, lust like the Prophet, and had "greater claims on them than their own selves."
al-Tirmidhi in his al-Sahih first relates this hadith, describing it as exalted and remarkable, and then further relates the Prophet, peace and blessings be upon him and his family, to have said: "'Ali is from me and I am from 'Ali; no one other than 'Ali has the right to do anything on my behalf," 
al-Hakim in his al-Mustadrak similarly relates the Messenger of God, peace and blessings be upon him and his family, to have said: "Whoever follows me has obeyed God, and whoever disobeys me has disobeyed God. Whoever obeys , 'Ali has obeyed me, and whoever disobeys , 'Ali has disobeyed me."
When therefore the Messenger of God, peace and blessings be upon him and his family, proclaims to the Muslims that, 'Ali, peace be upon him, has the same authority over the Muslims as himself, so that obedience to him is equivalent to obedience to the Messenger of God, he is in reality proclaiming 'Ali, peace be upon him, to the Muslim community as its overall leader and as the successor to his authority, calling on them to render him obedience.
One of the Shi'i scholars writes:
"I say in all sincerity that if the Prophet, peace and blessings be upon him and his family, had stood before the people on the day of Ghadir and said: 'For whomsoever I am his master, Abu Bakr is his master; O God, love those who love him and be hostile to those who are hostile to him,' I would be absolutely certain that the Prophet, peace and blessings be upon him and his family, had appointed Abu Bakr as his successor. Equally I cannot imagine that the vest mass of Muslims would have had any doubt that Abu Bakr had been appointed to the succession. If the Messenger of God, peace and blessings be upon him and his family, had said that Abu Bakr had greater claims on the believers than they did themselves and that adherence to the Qur'an was a sure protection against misguidance, there would be no room for hesitation.
"I wish to point out that the hesitancy of Muslims in agreeing that the hadith of Ghadir Khumm indicates the appointment of 'Ali, peace be upon him, by the Prophet, peace and blessings be upon him and his family, as his successor does not rest on obstinacy and fanaticism. It derives rather from the fact that they have grown up in a society where it is believed that the Prophet, peace and blessings be upon him and his family, did not appoint any successor. It is difficult for them to reconcile this belief with the clear meaning indicated by the hadith." 
Of course, one cannot reject the possibility that some of the Companions did not deliberately disobey the Prophet, peace and blessings be upon him and his family, when choosing his successor; they were simply mistaken in their calculations.
They imagined leadership and the rule of the ummah to be simply a worldly affair, so that it was permissible for them to overlook the one whom the Prophet, peace and blessings be upon him and his family, had selected and choose someone else to administer the public affairs of the ummah.
Such a group among the Companions may have imagined that the selection of 'Ali, peace be upon him, by the Prophet, peace and blessings be upon him and his family, was simply one of those matters of social concern on which the Prophet, peace and blessings be upon him and his family, would sometimes consult his Companions. If this is the case, they failed to grasp all the purposes that the Prophet, peace and blessings be upon him and his family, had in mind and the consequences he intended for his choice. Likewise they were incapable of reflecting on the disastrous consequences their own choice and decision would ultimately entail.
 Ibn Kathir, al-Bidayah, Vol.
V, pp. 209-13; al-Haythami, Majma' al-zawa'id, Vol. IX, pp. 163-5.
 al-Wahidi, asbab al-Nuzul,
p. 150; al-Suyuti, al-Durr al-Manthur, Vol. III, p. 298; al-Qunduzi,
Yanabi' al-Mawaddah, p. 130; al-Alusi, al-Tafsir, Vol. II,
p. 172; al-Shawkani, Fath al-Qadir, Vol. III, p. 57. Fakhr al-Din
al-Razi, al-Tafsir al-Kabir, Vol. III, p. 636; Badr al-Din
al-Hanafi, 'Umdah al-Qari, Vol. VIII, p. 584; Abduh, Tafsir al-Manar..
 Ahmad b. Hanbal, al-Musnad,
Vol. IV, p. 281; Ibn Kathir, al-Bidayah, Vol. V, p.212.
 Ahmad b. Hanbal, al-Musnad,
Vol. V, p. 181.
 al-Tirmidhi, Jami' al-Sahih,
Vol. V, p. 328.
 al-Muttaqial-Hindi, Kanz al-'Ummal,
Vol. XV, p. 123.
 Ahmad b. Hanbal, al-Musnad,
Vol. I, p. 118-19; al-Hakim, al-Mustadrak, Vol. III, p. 109; Ibn
Kathir, al-Bidayah, v, pp. 209, 213.
 al-Haythami, Majma' al-zawa'id,
Vol. IX, pp. 104-5; al-Hasakani, Shawahid al-tanzil, Vol. I, p.
193; Ahmad b. Hanbal, al-Musnad, Vol. I, p. 119. Ibn Kathir, al-Bidayah,
Vol. v, p. 212.
 The hadith concerning Ghadir
Khumm is to be found with various chains of transmission in the Sunni sources.
See al-Ghadir, Vol. I, pp. 14-72, where the hadith is reported
from 110 Companions of the Prophet, including Abu Bakr, 'Umar b. al-Khattab,
Ubayy b. Ka'b, Usamah b. Zayd, Anas b. Malik, Jabir b. 'Abdullah, Zayd
b. Arqam, Talhah, al-Zubayr, and Ibn Mas'ud. See too al-Tirmidhi, Jami
al-Sahih, Vol. II, p. 297. al-Hakim, al-Mustadrak, Vol. III,
p. 109; Fakhr al-Din al-Razi, al-Tafsir al-Kabir, Vol. XII,
p. 50; al-Wahidi, asbab al-Nuzul, p. 150; al-Suyuti, al-Durr
al-Manthur, Vol. II, p. 298; al-Ya'qubi, al-Tarikh, Vol. II,
p. 95; Ibn Kathir, al-Bidayah, Vol. V. al-Khatib al-Baghdadi, Tarikh
Baghdad, Vol. VII, p.377. al-Tha'labi, al-Tafsir, p. 120; Ibn
Hajar, Sawa'iq, Chapter 5.
 al-Suyut.i, al-Durr al-Manthur,
Vol. II, p. 256; Ibn Kathir, al-Bidayah, Vol. II, p. 14; al-Hamawini,
Fara'id al-simtayn, Chapter 12; al-Khatib al-Baghdadi, Tarikh
Baghdad, Vol. VIII, p. 290; al-Suyuti, al-Itqan, Vol. II, p.
31; al-Khwarazmi, al-Tarikh.
 al-Ya'qubi, al-Tarikh, Vol.
 Ibn Khallikan, Wafayat al-a'yan,
Vol. I, p.60.
 al-Mas'udi, al-Tanbih wa al-ishraf,
 al-Biruni, al-Athar al-Baqiyah,
(Persian translation), p. 334.
 Cited in al-Ghadir, Vol. I,
 For example, Qur'an, 57:15 and 22:13.
 Ahmad b. Hanbal, al-Musnad,
Vol. 1V, p. 281; Ibn Hajar, al-Sawa'iq, p. 26; al-Tabari, al-Tafsir,
Vol. III, p. 428; al-Ghazali, Sirr al-'alamin, p. 9. Fakhr al-Din
al-Razi, al-Tafsir al-Kabir, Vol. III, p. 636; al-Hamawini,
Fara'id al-simtayn, Chapter XIII; Ibn Kathir, al-Bidayah,
Vol. V, p. 209; Ibn Sabbagh, Fusul al-Muhimmah, p. 25; al-Muhibb
al-Tabari, Riyad al-Nadirah, Vol. II, p. 169.
 Sunni and Shi'i commentators alike
are agreed that this verse alludes to 'Ali.
 al-Tirmidhi, Jami' al-Sahih,
Vol. V, p. 300. See also Ibn Majah, al-Sunan, Vol. I, p. 44, and
Ahmad b. Hanbal, al-Musnad, Vol. IV, pp. 164-5.
 al-Hakim, al-Mustadrak, Vol.
III, p. 131.
 Amir al-Mu'minin.