Here the following question arises. Given the fact that the Prophet, peace and blessings be upon him and his family, proclaimed 'Ali to be his legatee (wasiyy) and successor (khalifah), emphatically designation him as the leader of the Muslims both at Ghadir Khumm and on other appropriate occasions, how did it happen that after the death of the Most Noble Messenger his Companions (sahabah) ignored God's command and abandoned 'Ali, that noble and precious personage, decided not to obey him, chose someone else to be leader in his place, and entrusted the reins of rule to him?
Was there any ambiguity in the words of the Prophet, or were all those different phrases and expressions establishing 'Ali's rank and designating him leader not enough?
A clear answer to this question can be found by examining the events that took place in the age of the Prophet, peace and blessings be upon him and his family. We see that there existed among his Companions elements who, whenever his commands ran contrary to their wishes and inclinations, pressed him to change his mind in the hope of preventing him, by whatever means possible, from carrying out his plans. When they despaired of reaching their goal, they would start complaining.
The Qur'an warns these people not to oppose the commands of the Prophet in the verse that reads: "Let those who oppose the commands of the Prophet fear disaster and a painful torment."(24:63)
During the last days of his blessed life, the Messenger of God prepared an army to do battle with the Byzantines and he appointed Usamah b. Zayd to be its commander. This appointment of a young man, despite the availability of older and more experienced men, proved displeasing to some of the Companions, and led to an argument among them. Those who were strongly oppossed to Usamah b. Zayd asked the Prophet to dismiss him, but he paid no attention to their request and commanded Abu Bakr, 'Umar and 'Uthman to join the ranks of the Muslim army as it departed from Madinah. However, they not only disregarded military discipline but also disobeyed the categorical command of the Prophet. Instead of proceeding to the front with the army, they split off and returned to Madinah. 
The disrespectful mumblings of some of the Companions greatly vexed the Messenger of God, peace and blessings be upon him and his family, and with a heart full of pain and concern for his people, he came forth from his house and addressed the people as follows:
"O people, what are these words of yours concerning the appointment of Usamah that have come to my ears? Just as you are criticizing him now, you once objected to the appointment of his father Zayd b. al-Harithah as commander. I answer by God that just as he was worthy of command, so too is his son." 
Even after the death of the Prophet, 'Umar came to Abu Bakr and demanded that he should dismiss Usamah. The caliph replied: "The Messenger of God appointed him, and you wish me to dismiss him?" 
The Prophet's wish and desire during the final days of his life was to empty Madinah of the leaders of both the Emigrants and the Helpers. He therefore has Usamah's army prepared for battle and gave the command for jihad, ordering the army to advance in the direction of the Syrian border. Insistently he asked the foremost of the Companions to leave Madinah and fight under the banner of Usamah, retaining only 'Ali to stay at his bedside. This remarkable act on the part of the Prophet was very significant. However, those Companions failed to comply with his instructions, and they withdrew from the army commanded by Usamah.
Throughout his life, the Prophet never appointed anyone as commander over the head of 'Ali, peace be upon him; it was always he who was the standard bearer and commander.  By contrast, Abu Bakr and 'Umar were to be simple soldiers in the army of Usamah, and the Prophet personally ordered them to serve under him when he appointed him commander at the battle of Mu'ta. Historians are unanimously agreed on this point. Likewise, at the Battle of Dhat al-Salasil, when the army was commanded by Ibn al-'As, Abu Bakr and 'Umar again served as simple soldiers. This contrasts with the case of 'Ali b. Abi Talib, whom the Prophet, from the beginning of his mission until his death, never made subordinate to anyone, an extremely significant point.
History will never forget the time when the Most Noble Messenger, peace and blessings be upon him and his family, was on his deathbed, his state becoming progressively more grave. He felt that the last strands of his life were being plucked apart. He therefore decided without further delay to put his final plan into effect and said: "Bring me paper so that I can write for you a document to prevent you from ever going astray." 
Just as he had clarified the question of leadership in numerous speeches and utterances, he wished now, one final time, to address this weighty matter, described by the Qur'an as the completion of religion, by enshrining it in an authoritative written document to remain among the Muslims after his death. Thereby the door would be closed on any future deviations from his orders. But those same people who in defiance of his orders had refrained from going to the front were now watching the situation carefully with the intention of implementing their plans at the first possible opportunity. They therefore refused to permit writing utensils to be brought to the Prophet. 
Jabir b. Abdullah says:
"When the Messenger of God fell sick with the illness that was to end in his death, he asked for paper in order to write down for his ummah instructions that would prevent them from ever going astray or accusing each other of having gone astray. Words were exchanged among those present in the Prophet's house and an argument ensued in the course of which 'Umar uttered words that caused the Prophet to order him to leave the house." 
'Ubaydullah b. Abdullah b. 'Utbah relates Ibn Abbas to have said:
"During the final moments of the life of the Messenger of God, peace and blessings be upon him and his family, a number of people were present in this house, including 'Umar b. al-Khattab, The Prophet said: 'Come, let me write for you a document that will prevent you from ever going astray after me.' 'Umar said: 'Sickness has overcome the Prophet; we have the Qur'an, which is enough for us.'
"Then disagreement arose among those present. They began to argue with each other, some saying, 'Quick, have the Prophet write a document for you so that you will never go astray after him,' and others repeating the words of 'Umar.
"When the arguing and nonsensical talk reached its pitch, the Prophet, peace and blessings be upon him and his family, told them all to leave."
Thus it was that, as Ibn Abbas says: "The great misfortune arose when their noisy disputing prevented the Messenger of God from writing his testamentary document."  He then adds sorrowfully. "The tribulations of the Muslims began on that very day." 
In the discussion that took place between Ibn Abbas and the second caliph concerning the caliphate of 'Ali, the caliph said: "The Prophet wanted to declare 'Ali as his successor, but I did not allow it to happen." 
Some Sunni historians and hadith scholars have written that when the Prophet decided to write a document that would prevent the Muslims from going astray 'Umar said: "The Messenger of God has become delirious." Others, however, in order to soften the offensiveness of his words, maintain that he said: "Sickness has overcome the Prophet; you have the Book of God at your disposal, which is enough for us." 
It seems that the Most Noble Messenger, peace and blessings be upon him and his family, was unaware of the importance of the Book of God and they were better informed than him on this point! Was it necessary to accuse him of mental derangement if he wished to draw up a written document specifying who was to lead the ummah after his death? If indeed the Prophet's decision could be attributed to the failing of his mental powers as a result of illness, why did the second caliph not prevent Abu Bakr from drawing up a comparable document during the last moments of his life, or accuse him of being deranged? 'Umar was present at the side of Abu Bakr and he knew that Abu Bakr intended to designate him as ruler in his testament, so naturally he wanted the document to be signed.
If 'Umar truly thought the Book of God to suffice for the solution of all problems, why did he immediately hasten to the Saqifah after the death of the Prophet, together with Abu Bakr to ensure that the question of the caliphate should be resolved in accordance with their ideas? Why did they not at that point refer exclusively to the Book of God and make no mention of the Qur'an, even though the Qur'an had already settled the matter?
al-Tabari writes the following in his history:
"When Shadid, the emancipated slave of Abu Bakr took into his hand the command Abu Bakr had written for 'Umar to become his successor, 'Umar said to the people, "People, pay heed, and obey the command of the caliph. The caliph says, 'I have not failed you in providing for your welfare.'" 
The expression of personal opinions running counter to the orders of the Prophet, peace and blessings be upon him and his family, continued after his death, culminating in the changing of certain divine decrees in the time of the second caliph and on his orders. Instances of this are to be found in reputable books by Sunni authors. 
For example, the second caliph said: "Let them never bring before me a man who has married a woman for a set period, for it they do I will stone him."  The fact that he prohibited temporary marriage (mut'ah) proves that this type of union was common among the Companions and other Muslims at the time, for otherwise it would not have been necessary for him to order them to desist. Now if the Messenger of God, peace and blessings be upon him and his family, had forbidden this form of marriage, the Companions would never have had recourse to it and there would have no need for 'Umar to threaten people with stoning.
The second caliph himself admitted: "There were three things that were permissible in the time of the Prophet which I have forbidden and for which I exact punishment: temporary marriage, the mut'ah pilgrimage, and reciting 'Hasten to the best of deeds' (hayya 'ala khayri 'l-'amal) in the call to prayer."
It was also he ordered that in the call to prayer (adhan) at dawn the phrase, "prayer is better than sleep" (as 'salatu khayrun mina 'n-nawm) should be recited. 
According to the Sunan of al-Tirmidhi someone from Syria once asked 'Abdullah b. 'Umar about the mut'ah pilgrimage. He replied that it was permissible. When the man remarked that Abdullah's father had prohibited it, he answered, "If my father has forbidden something which the Prophet, peace and blessings be upon him and his family, permitted, should we abandon the Sunnah of the Prophet and follow my father?" 
Ibn Kathir similarly records in his history: "Abdullah b. 'Umar was told that his father had prohibited the mut'ah pilgrimage. He said in reply: 'I fear that a stone will fall on you from the heavens. Are we to follow the Sunnah of the Prophet or the Sunnah of 'Umar b. al-Khattab?'" 
During the time of the Prophet, peace and blessings be upon him and his family, as well as the caliphate of Abu Bakr and the first three years of the caliphate of 'Umar, if anyone were to divorce his wife three times on a single occasion, it counted as a single repudiation, and was not therefore final. However, 'Umar said: "If such a repudiation is made, I will count it as a threefold (and therefore final) repudiation." 
The Shi'ah believe that such a repudiation (talaq) counts only as a single repudiation, and Shaykh Mahmud al-Shaltut, erstwhile rector of the Azhar, regarded Shi'i jurisprudence (fiqh) superior in this respect as well as many others. 
No one has the right to tamper with revealed ordinances, for they are divine and immutable, not even the Prophet himself. The Qur'an says: "Were Muhammad to attribute lies to Us, with Our powerful hand We would seize him and cut his jugular vein."(69:44)
However, we see that unfortunately some of the Companions awarded themselves the right of exercising independent judgement (ijtihad) with respect to certain ordinances, changing and modifying divine law in accordance with their own notions.
The second caliph introduced class differences into Islamic society during the time of his rule, increasing racial tensions between the Arabs and the Persians.  He established a discriminatory system of distributing public monies, awarding more to those who accepted Islam early on than to those who embraced it later; more to Qurayshite Migrants than to non-Qurayshite Migrants; more to the Migrants than to the Helpers; more to the Arabs than to the non-Arabs; and more to masters than to their clients. 
Toward the end of his life 'Umar himself came to recognize the negative effects of his policy and he said: "If I remain alive this year, I will establish equality in Islamic society and abolish discrimination. I will act in the way the Messenger of God, peace and blessings be upon him and his family, and Abu Bakr both acted." 
The foregoing indicates the arbitrary attitude that some of the Companions assumed with respect to the commands of the Prophet. In certain cases where those commands did not correspond to their personal inclinations, they tried either to avoid implementing them or to change them completely. The fact that they ignored the unmistakably authoritative utterances of the Prophet on the day of Ghadir Khumm or that they behaved similarly with respect to other matters after his death, should not be regarded as either surprising or unprecedented, for they had already given an indication of their attitudes during his lifetime.
In addition, it should not be forgotten that in every society most people tend to remain indifferent to political and social matters, choosing to follow their leaders and those who seize the initiative. This is a clear and undeniable fact.
However, there were respectable and independent minded people who did not change their position after the death of the Prophet. They did not approve of the election that took place at the Saqifah, and they separated themselves from the majority in protest against the introduction of the consultative concept into Islamic government. Although they were more or less compelled to remain silent, they remained loyal to 'Ali b. Abi Talib, peace be upon him, as leader. Among the outstanding personalities belonging to this group were Salman al-Farisi, Abu Dharr al-Ghifari, Abu Ayyub al-Ansari, Khuzaymah b. Thabit, Miqdad b. al-Aswad, al-Kindi, 'Ammar b. yasir, Ubayy b. Ka'b, Khalid b. Sa'id, Bilal, Qays b. Sa'd, Aban, Buraydah al-Ashami, Abu 'l-Haytham b. al-Tayyihan, as well as many others whose names are recorded in Islamic history. Some scholars have listed two hundred and fifty Companions of the Prophet, complete with names and descriptions, as belonging to this class. 
al-Ya'qubi mentions in his history Abu Dharr al-Ghifari, Salman al-Farisi, Miqdad b. al-Aswad, Khalid b. Sa'id, Zubayr, 'Abbas, Bara' b. Azib, Ubayy b. Ka'b, and Fadh b. al-'Abbas as being among those who remained loyal to the cause of 'Ali, peace be upon him. Qays b. Sa'd even went so far as to argue with his father over the question of the caliphate and he swore never to speak to him again because of this views.
These are some of the earliest Shi'is; they supported 'Ali's right to the leadership because of the clear injunctions in the Qur'an and the Sunnah. They remained unswerving in their views until the end. During the period of the first three caliphs the number of Shi'is in fact rose, all of them being outstanding and virtuous personalities, their names being linked to piety and purity in the books of history and biography where they are mentioned. Among them were men such as Muhammad b. Abi Bakr, Sa'sa'ah b. Suhan, Zayd b. Suhan, Hisham b.'Utbah, Abdullah b. Budayl al-Khuza'i, Maytham al-Tammar,' Adiyy b. Hatim, Hujr b. Adiyy, Asbagh b. Nubatah, al-Harith al-A'war al-Hamdani, Amr b. al-Humq al-Khaza'i, Malik al-Ashtar, and Abdullah b. Hashim.
 Ibn Hisham, al-Sirah, Vol.
IV p. 338; al-Ya'qubi, al-Tarikh, Vol. II, p.92; Ibn al-Athir, al-Kamil,
Vol. II, pp. 120-21.
 Ibn Sa'd,al-Tabaqat, Vol.
 al-Halabi, al-Sirah, Vol.
 Ibn Sa'd, al-Tabaqat, Vol.
III, p. 25; al-Hakim, al-Mustadrak, Vol. III, p. 1.
 Ahmad b. Hanbal, al-Musnad,
Vol. I, p.346; Muslim, al-Sahih, Vol. V, p. 76; al-Tabari, Tarikh,
Vol. II, p. 436; Ibn Sa'd, al-Tabaqat, Vol. II, p.242.
 al-Bukhari, al-Sahih, Vol.
I, p. 22; al-Tabari, al-Tarikh, Vol. II, p. 436; Muslim, al-Sahih
., Vol. V, p. 76; Ahmad b. Hanbal, al-Musnad, Vol. III, p.346.
 Ibn Sa'd, al-Tabaqat, Vol.
II, p. 243.
 Ibn Sa'd, al-Tabaqat, Vol.
II, p.242; Muslim, al-Sahih, Vol. XI, p. 95; Ahmad b. Hanbal, al-Musnad,
Vol. I, p. 336.
 Ibn Kathir, al-Bidayah, Vol.
V, pp. 227-28; al-Dhahabi, Tarikh al-Islam, Vol. I, p. 311; al-Diyar
Bakri, Tarikh al-Khamis, Vol. I, p. 182; al-Bid'wa al-Tarikh,
Vol. V, p. 95; Taysir al-Wusul, Vol. IV, p. 194.
 Ibn Abi 'l-Hadid, Sharh .,
Vol. III, p.97.
 Muslim, al-Sahih, Vol. III,
p. 1259; al-Bukhari, al-Sahih, Vol. IV , p. 5; Ahmad b. Hanbal,
al-Musnad, hadith no. 2992.,
 al-Tabari, Tarikh, Vol. IV,
 Ibn Hisham, al-Sirah, Vol.
IV, p. 237; Muslim, al-Sahih, Vol. IV, pp. 37-8, 46; al-Tabari,
Tarikh, Vol. II, p. 401; Ahmad b. Hanbal, al-Musnad, Vol.
III, pp. 304, 380.
 Muslim, al-Sahih, Vol. VIII,
 al-Amini, al-Ghadir, Vol.
 Ahmad b. Hanbal, al-Musnad,
Vol. III, p. 408; Muslim, al-Sahih, Vol. III, p. 183; al-Halabi,
al-Sirah, Vol. II, p. 105; Ibn Kathir, Vol. III, p.23.
 al-Tirmidhi, Jami' al-Sahih,
Vol. IV, p.38.
 Ibn Kathir, al-Bidayah, Vol.
V, p. 141.
 Muslim, al-Sahih, Vol. IV,
 Risalat al-Islam, Vol. XI,
 al-Ya'qubi, al-Tarikh, Vol.
II, p. 107.
 Ibn Abi 'l-Hadid, Sharh, Vol.
VIII, p. 11; Ibn Sa'd, al-Tabaqat, Vol. III, pp. 296-7.
 Taha Husayn, al-Fitnat al-Kubra,
Vol. I, p. 108.
 al-Sayyid Sharaf al-Din, Fusul
al-Muhimmah, pp. 177-92.
 al-Ya'qubi, al-Tarikh,
Vol. II, p. 103.
 Ibn Abi 'l-Hadid, Sharh, Vol. II, p. 18.