Some people ask why at the meeting held in the Saqifah 'Ali, peace be upon him, did not raise the issue of his appointment at Ghadir Khumm by the Messenger of God, peace and blessings be upon him and his family, to be his successor. Why, they ask, did he not tell the Migrants and the Helpers that he had been appointed by the Prophet so that nobody had the right to contest the succession with him or to claim the caliphate? Had the thousands of people who had been present at Ghadir Khumm forgotten what they had witnessed?
The answer is that the Imam did indeed raise the issue of Ghadir Khumm whenever he deemed it appropriate in order to prove the justice of his claim to the successorship and to object to the decision that had been taken at the Saqifah, thus reminding people of what had happened. For example, historians relate the following:
"When Fatimah, the daughter of the Prophet, peace and blessings be upon him and his family, together with 'Ali, peace be upon him, sought aid from the Companions, they answered, O daughter of the Messenger of God! We have given our allegiance to Abu Bakr. If 'Ali had come to us before this, we would certainly not have abandoned him.' 'Ali, peace be upon him, them said, 'Was it fitting that we should wrangle over the caliphate even before the Prophet was buried?' 
Similarly, on the day that the six-man council was convened and 'Abd al-Rahman b. 'Awf made plain his inclination that 'Uthman be appointed caliph, the Imam said: "I will set before you an undeniable truth. By God, is there any among you concerning whom the Prophet, peace and blessings be upon him and his family, said, 'For whomsoever I was until now the master, henceforth 'Ali is the master; O Lord, love whoever loves 'Ali and help whoever helps 'Ali,' ordering this to be conveyed to those who were absent?" All the members of the council confirmed the truth of the words he had spoken, saying, "none can lay claim to any of this." 
It is an indisputable historical fact that thirty of the Companions testified at the congregational mosque in Rahbah to what they had witnessed at Ghadir Khumm. The historians relate that one day 'Ali, peace be upon him, said in the course of a sermon he was delivering at this mosque, "O Muslims, I adjure you by God: is there among you any who witnessed what transpired at Ghadir Khumm, who heard the Messenger of God, peace and blessings be upon him and his family, proclaiming me to be his successor, and who observed the people paying allegiance to me? Stand up and give witness!"
At this point thirty men out of those present stood up and in a loud voice testified to what they had seen at Ghadir Khumm.
Another telling of this same incident relates: "Many people stood up to give witness." 
This testimony to what had transpired at Ghadir Khumm was given at the mosque in Rahbah during the caliphate of 'Ali, peace be upon him, in the thirty-fifth years of the Hijrah, while the proclamation of 'Ali's successorship at Ghadir Khumm in the course of the Farewell Pilgrimage had taken place in the tenth year of the Hijrah, i.e., twenty five years earlier. 
Taking into consideration the fact that many elderly Companions must have died during this quarter century, that many casualties had been incurred during the wars that took place during the rule of the first three caliphs, and that many surviving Companions were not present in Kufah, being scattered in other cities, the significance of this historic testimony to what had happened at Ghadir Khumm is obvious. Ahmad b. Hanbal writes: "Only three men did not rise to their feet, although they too had been present at Ghadir Khumm. 'Ali, peace be upon him, cursed them and they were afflicted." 
Abu al-Tufayl says: "When I left the mosque at Rahbah I asked myself how the majority of the ummah had failed to act in accordance with the hadith of Ghadir Khumm. I met Zayd b. Arqam to discuss the matter with him and told him, 'I heard 'Ali, peace be upon him, say such-and-such.' Zayd replied, 'The truth of what he says is undeniable; I too heard it from the Prophet, peace and blessings be upon him and his family." 
'Ali, peace be upon him, adduced the hadith of Ghadir Khumm in support of his claims on numerous other occasions. He cited it as proof of his Imamate during the Battle of the Camel, at Siffin and in Kufah, as well as in the Mosque of the Prophet, peace and blessings be upon him and his family, in Madinah on an occasion when two hundred leading persons from among the Migrants and Companions were present. 
Apart from this, various factors prevented 'Ali, peace be upon him, from reacting strongly to what occurred at the Saqifah and caused him to choose the path of endurance and patience instead, a patience he himself described as akin to having "a thorn in the eye and a bone in the throat." 
It will be apposite here to cite some passages from the answer of the late Allamah Sharaf al-Din to Shaykh Salim al-Bishri:
"Everyone knows that the Imam and his friends from among the Bani Hashim and other tribes were not present at the Saqifah when allegiance was being sworn to Abu Bakr; in fact, they had not even set foot there, being engaged in the imperative and grave task of preparing the Prophet, peace and blessings be upon him and his family, for burial and being unable to think of anything else.
"The ceremonies of the Prophet's burial were still not over when the people gathered at the Saqifah completed their business. They gave allegiance to Abu Bakr, swore loyalty to him, and with remarkable farsightedness agreed to confront firmly any development threatening to weaken the state.
"Was 'Ali, peace be upon him, in any position then to argue his case before the people? And was he given any chance to do so once allegiance had been sworn to Abu Bakr? His opponents displayed cunning and political acumen and neither did they shrink from violence. Even in our age, how many people find it possible to rise up in revolt against the government or to overthrow it simply by popular pressure? And if someone has the intention of doing so, will he be left untroubled?
"If you compare the past with the present, you will see that people were just the same as they are now, that conditions then were just the same. Moreover, if 'Ali, peace be upon him, had raised his claim at that time, the only result would have been confusion and disorder, and he would still have been unable to assert his rights. For him, the preservation of the foundations of Islam and of the doctrine of divine unity was an overarching aim. The ordeal that 'Ali, peace be upon him, underwent at that time tried him sorely. Two momentous matters were weighing on him. On the one hand. his explicit designation as caliph (khalif) and legatee (wasiyy) of the Prophet, peace and blessings be upon him and his family, was still ringing in his ears and impelling him to act. On the other hand, the disturbances and rebellions that were arising on all sides served to warn him that the situation in the entire Arabian peninsula might collapse; the people might change their attitudes altogether, leading to the disappearance of Islam. He was in addition threatened by the existence of the Hypocrites in Madinah who had grown in strength after the death of the Prophet, peace and blessings be upon him and his family. The Muslims at that time were like a flock of sheep stranded by a flood on a dark winter's night, surrounded by bloodthirsty wolves and predators.
"Musaylamah al-Kadhdhab, Talhah b. Khuwaylid and Sijah the daughter of al-Harith, together with the rabble that had gathered around them, were exerting themselves to the utmost to destroy Islam and vanquish the Muslims.
"As if all this were not enough, the Persian and Byzantine emperors, as well as the other powerful rulers of the age, were waiting for a favorable opportunity to attack Islam. Many others too, in their hatred for the Prophet, peace and blessings be upon him and his family, and his Companions were ready to use any means in order to avenge themselves on Islam, and they saw in the death of the leader of Islam a favorable opportunity for causing sabotage and destruction.
"'Ali thus found himself at a crossroads, and it was natural that one of his caliber should sacrifice his own right to the caliphate to the cause of Islam and the Muslims. However, even while sacrificing his right, he wished to adopt an appropriate stance to those who had usurped it, one that did not lead to disorder or disunity among the Muslims or create an opportunity for the enemies of Islam. He therefore remained at home and did not swear allegiance to Abu Bakr until he was forced to leave his home and brought to the mosque. If he had gone of his own accord to swear allegiance, he would have effectively relinquished his claim to the caliphate and his partisans would have been left without any argument to make on his behalf. By choosing the path that he did, he accomplished two things: the preservation of Islam and the safeguarding of the legitimate form of the caliphate. He acted thus because he realized that under the circumstances the preservation of Islam depended on his making peace with the caliphs. He was motivated solely by the desire to protect the shari'ah and religion; in fact, in renouncing the office that was rightly his for the sake of God he was acting in accord with the duty prescribed by both reason and religion giving priority to the more important of two contradictory duties.
"In short, the situation prevailing at the time made it impossible for him either to take up the sword in rebellion or to argue for his rights and criticize the state of affairs in the young Muslim community. Nonetheless, 'Ali and his progeny, peace be upon them, as well as scholars devoted to his cause have always found intelligent and appropriate ways of reminding the Muslim community of the instructions left by the Prophet, peace and blessings be upon him and his family, at Ghadir Khumm. As all scholars are aware, they ceaselessly propagated the relevant traditions of the Prophet, peace and blessings be upon him and his family " 
 Ibn Qutaybah, al-Imamah wa al-Siyasah,
Vol. I, pp. 12-13; Ibn Abi al-Hadid, Sharh; Vol. II, p.5.
 al-Khwarazmi, al-Manaqib,
 al-Muhibb al-Tabari, Riyad al-Nadirah,
Vol. II, p. 162; Ibn Kathir, al-Bidayah, Vol. V, p. 212; Ahmad b.
Hanbal, al-Musnad, Vol. I, pp. 118-19.
 Ahmad b. Hanbal, al-Musnad,
Vol. IV, p. 370; Ibn Kathir, al-Bidayah, Vol. V, p. 212.
 Ahmad b. Hanbal, al-Musnad,
Vol. IV, p. 370. See also Ibn Qutaybah, Kitab al-Ma'arif, p. 194.
 Ibn Majah, al-Sunan, Vol.
IV, p. 370.
 al-Hamawini, Fara'id al-simtayn,
 See the "Khutbah Shaqshaqiyyah"
in al-Radi's Nahj al-Balaghah.
 Sharaf al-Din, al-Muraja'at, (Persian translation), p. 429.