No event in history has divided Islam more profoundly and durably than the succession to Muḥammad. The right to occupy the Prophet's place at the head of the Muslim community after his death became a question of great religious weight which has separated Sunnites and Shi'ites until the present. The issue of right and wrong in the matter has long since been settled in their minds. For Sunnites, the first caliph, Abū Bakr, was the only rightful successor since he was the most excellent of men after the Prophet. Although Muḥammad had not explicitly appointed him as his successor, his preference for him was indicated by his order for Abū Bakr to lead the Muslims in the prayers during his final illness. The consensus reached by the Muslims in favour of Abū Bakr merely confirmed what was ultimately God's choice. For Shi'ites it was Muhammad's cousin and son-in-law 'Alī who, on account of his early merits in Islam as well as his close kinship, had been appointed by the Prophet as his successor. His rightful position was then usurped by Abū Bakr with the backing of the majority of Muḥammad's Companions.

In spite of the fundamental importance of this conflict for the history of Islam, modern historians have devoted relatively little effort to the study of the background and circumstances surrounding the succession. This general lack of interest is evidently grounded in the view that the conflict between Sunna and Shī'a, although revolving around the question of the succession, in reality arose only in a later age.