The succession to Muhammad is the key question in Shiite Islam, and a principal factor separating them from the Sunni majority. It is seen that Muhammad had nominated Ali bin Abu Talib as his successor by rule of nass (investiture) and nass wa-ta'yin (explicit investiture). During the period of the Prophethood, the designation was made by nass from time to time, whose main term was wali (helper, friend, lover, guardian or attorney), as it is said in Arabic: wali amru'l raiyya(the guardian of the subject), or wali ahad (one who succeeds to the office). In addition to the wali, different terms were used on different occasions for the succession of Ali bin Abu Talib in Holy Koran, such as Noor, Imam-i Moobin, Rasikhul fi'l Ilm, Ulil Amr, Ilmul Kitab etc. While the most frequent words used in Hadiths, denoting Ali's succession were hujjatullah (God's proof), Sayedu'l Muslimin (leader of the Muslims), Shabih Harun (like Aaron), Sahibu'l lawa (the master of the standard), Sahibu'l hanz (master of Kauthar pool), Babu'l Ilm (gate of the knowledge) etc.
The nass wa-ta'yin was made after the farewell pilgrimage of Muhammad. Accordingly, on Monday, the 20th Zilkada, 10, Muhammad received following revelation:-
Due proclamation was made among the Muslims to join the pilgrimage, and Muhammad himself left Medina on Saturday, the 25th Zilkada, 10 which was his farewell pilgrimage. He reached Mecca on Wednesday, the 7th Zilhaja, 10, and performed the pilgrimage. He delivered a historical sermon at the plain of Arfat. He left Mecca on 14th Zilhaja, 10 after performance of pilgrimage. His caravan reached a little before noon to a pond (ghadir), known as Khum, on 18th Zilhaja, 10/March 16, 632. It is situated about 3 miles north-west of Mecca in the heart of the desert, called Sahara'i Huja, about 3 miles from the town, al-Jahfa. Here, Muhammad received the following Koranic revelation:-
The town al-Jahfa was a junction from where the routes for Medina, Egypt, Syria and Iraq radiated in different directions. On its border is a pond (ghadir) with a vast open plain, embosomed with trees and bushes, which had been swept off. Under the shade of two trees, a big pulpit for Muhammad was erected with the camel-saddles. He mounted it and placed Ali on his right. He then delivered a sermon, thanking God for His bounty and stated that he felt that he would die soon. He repeated that he would be leaving two heavy weights i.e., Holy Koran and his Ahl-al-Bait, with them. The two were inseparable. If people held both fast they would never go astray. Muhammad then asked his audience if he was not superior to the believers. The crowd answered in the affirmative. He then declared: "Whose Master (mawla) I am, this Ali is his Master (mawla)." He then prayed, "O God, be the friend of him who is his friend, and be the enemy of him who is his enemy." After the sermon, Muhammad dismounted and retired to his tent. He asked Ali to accept the people's congratulation and allegiance.
It must be known that the word mawla means master, lord, guardian or one who deserves superior authority. As the words ana awla (I am superior) indicate that mawla means awla (superior). What Muhammad meant by this sentence was, God is superior in right and might to him and he is superior in right and might to the faithful and Ali is superior in right and might to all those to whom Muhammad is superior.
The most earliest source of the event of Ghadir'i Khum is Asma bint Umays (d. 38/658), the wife of Jafar Taiyar bin Abu Talib. Her report has been documented in "at-Tarikh" (Beirut, 1960) by the historian Yaqubi (d. 284/898). Hassan bin Thabit (d. 40/661), a famous poet had vividly versified the event in his Diwan of 228 poems. Suleman bin Qays al-Hilali (d. 82/701) also is ranked among the earliest authorities. Kumyt bin Zaid (60-126/680-744) however has been considered as the most earliest authority by the German scholars, Horovitz and Goldzier. Among the prominent Companions, who had related the event of Ghadir'i Khum are Abuzar Ghafari (d. 32/653), Huzaifah al-Yameni (d. 29/650), Abu Ayub Ansari (d. 50/670), Ammar bin Yasir (d. 37/657), Salman al-Faras (d. 36/657), Abdullah bin Abbas (d. 86/705) etc. etc. Among the earliest Umayyad historians, the most famous were Ibn Shihab az-Zuhari (50-125/670-744) and Ibn Ishaq (d. 152/769).
The historians and compilers of the Hadiths between 10/632 and 300/912 were mostly under pressure of the ruling powers of Umayyads and the Abbasids, therefore, they avoided to refer the event, such as Ibn Hisham (d. 218/833), Ibn Sa'd (d. 230/845) and Tabari (d. 310/922). Nevertheless, Nisai (d. 151/768), Ahmad bin Hanbal (d. 241/855), Tirmizi (d. 279/893), Ibn Majah (d. 283/897), Abu Daud (d. 276/890) and Yaqubi (d. 284/898) had demonstrated their impartiality, whose bold assertion lends colour to this historical event. In sum, Hussein Ali Mahfuz, in his researches, has recorded with documentation in "Tarikh ash-Shia" (Karbala, n.d., p. 77) as quoted by Dr. S.H.M. Jafri in "Origins and Early Development of Shia Islam" (London, 1979, p. 20) that the tradition of Ghadir'i Khum has been narrated by at least 110 Companions, 84 tabi'un, 355 ulema, 25 historians, 27 traditionists, 11 exegesists, 18 theologians and 5 philosophers.
It must however be remembered that the Arabs of Northern and Central, of whom the tribe of Qoraish was dominant in Mecca. The people of South Arabian origin, Banu Aws and Banu Khazraj had settled in Medina. There had been many differences among the Arabs of North and South, socially, culturally, economically, geographically and religiously. The leader in the North was elected on a principle of seniority in age with administrative ability. In South, the Arabs were accustomed to hereditary succession in leadership. In the face of these facts, the South Arabian tribes of Aws and Khazraj had presented a healthy atmosphere for Islam in Medina. The majority of Northern Arabs were nomads, and understood Islam at least at the first stage of their acceptance of it as social-political discipline, as the Holy Koran says: "The wandering Arabs are harder in disbelief and hypocrisy and more likely to be ignorant of the limits which God has revealed to His Prophet" (9:97). These Arabs of North have been also called "most obdurate in hypocrisy" (9:101). Conversely, the tribes of Aws and Khazraj had understood Islam as basically religious discipline couped with a socio-political movement, and were more sensitive to religious affairs. When the Holy Prophet died in 10/632, the issue of his succession was understood to combine it both political and religious leadership. To some it was more political than religious, to others it was more religious than political. The majority who accepted Abu Bakr as their leader, had laid more emphasis on the socio-political side, disregarding the religious principle and the idea of hereditary sanctity of a certain house. This assumption is strongly supported by the words of Umar bin Khattab, who in reply to Ibn Abbas, said: "The people do not like having the Prophethood and Caliphate combined in the Banu Hashim" (Tabari, 1st vol., p. 2769). Hence, Muhammad did not designate Ali explicitly in the start owing to the Northern Arabian custom of leaving the selection of a leader to the people. The Holy Koran however says that Muhammad's family had a prerogative over others. Neither Banu Taym bin Marra, the clan of Abu Bakr, nor Banu Adi bin Ka'b, the tribe of Umar Khattab had ever been regarded with esteem on any religious ground. But, those who laid stress on the religious principle could not accept them as candidates for succession to Muhammad. It was from Banu Hashim, and among them was only Ali bin Abu Talib for the succession.
There was an assembly hall (saqeefa), about 6 miles from Medina, belonging to Banu Sa'd, where the Arabs used to discuss their mutual problems. Upon the death of Muhammad, the Ansars and Muhajirs of Medina, numbering about 300 to 325, had assembled at Saqeefa Banu Sa'd to choose their leader. There was not a single man from Banu Hashim. Abu Bakr and Umar bin Khattab also rushed the spot during the time when the people were about to take an oath of allegiance from Abu Ubaida as their caliph. The proceeding stopped and a hot argument started among them. Historian Tabari (3rd vol., p. 198) writes, "The Ansars or some were arguing that they would never take oath from anybody except Ali". When the swords were about to unshield, Umar bin Khattab asked Abu Bakr to raise his hand, and took his bayt, then it was followed by Abu Ubaida and the rest of people.
Sir Thomas W. Arnold writes in "The Caliphate" (London, 1924, p. 30) that, "The Prophet had been at one and the same head of the state and head of the church. The paramount control of political policy was in his hands; he received the ambassadors who brought the submission of the various Arab tribes, and he appointed officers to collect dues and taxes. He exercised supreme authority in military matters and the dispatch of military expeditions. He was at the same time supreme legislator, and not only promulgated legal status, but set in judgement to decide cases, against his decision there was no appeal. In addition to the performance of these offices of administrative and political order as ruler, general and judge, he was also revered as the inspired Prophet of God and the religious dogmas he enunciated were accepted by his followers as revelations of divine truth, in regard to which there could be no doubt or dispute. At the same time he performed the highest ecclesiastical functions, and as Imam led the prayer in public worship at the canonical hours in the mosque of Medina. In all these respects, Abu Bakr was a successor of the founder of the faith - with the exception of the exercise of the prophetic function." In sum, Muhammad administered both temporal and spiritual powers in Islam, and after his death, the temporal power came to the hands of Abu Bakr in the form of Caliphate, while the spiritual power was inherited by Ali bin Abu Talib and his descendant in the form of Imamate.
During the period of Abu Bakr's caliphate, whatever initial support there may have been for Ali's candidature melted away in the face of Ali's own refusal to advance the temporal claim. Ali reverted to leading a quiet life, almost confined to the four walls of his house. He had no choice but to reconcile himself with the existing order, since he had considered that any action would lead to the destruction of infant Islam. His compromise with the political order can be well asserted from the fact that he did not demonstrate any sort of opposing attitude publicly and continued to live in Medina. If he had quitted Medina for elsewhere, his followers supporting his cause, must have followed him, which Ali most probably did not like.
Tabari (3rd vol., pp.203-4) writes that Abu Sufian bin Harb, who endeavoured to instigate Ali with the words: "What! It is the limit that in your presence, one of the lowliest families of Arabia should have gained the upper hand. By God, if you so desire I would fill the streets and lanes of Medina with mounted soldiers to aid you." Ali gave him short shift reply that, "By God, you have always been an enemy of Islam and of the Muslims." This demonstrated how firmly Ali was resolved to place the collective interests of the community and solidarity of Islam. In spite of maintaining his passive attitude, Ali did occasionally help the caliphs. He was a valued counsellor of the caliphs, and dominated by his heroic love and sense of sacrifice for the faith and saved the caliphs from committing the serious mistakes. Umar is thus often reported to have said: "Had there not been Ali, Umar would have perished."