Abu Bakr's assumption of power is an extremely controversial matter, and the source of the first schism in Islam, between Sunni and Shia Islam. Shi'a believe that Muhammad's cousin and son-in-law, Ali ibn Abu Talib, was his designated successor, while Sunnis believe that Muhammad deliberately declined to designate a successor. They argue that Muhammad endorsed the traditional Arabian method of shura or consultation, as the way for the community to choose leaders. Designating one's successor was the sign of kingship, or mulk, which the independence-minded tribesmen disliked. Whatever the truth of the matter, Ali gave his formal bay'ah, or submission, to Abu Bakr and to Abu Bakr's two successors. (The Sunni depict this bay'ah as enthusiastic, and Ali as a supporter of Abu Bakr and Umar; the Shi'a argue that Ali's support was only pro forma, and that he effectively withdrew from public life in protest). The Sunni/Shi'a schism did not erupt into open warfare until much later. Many volumes have been written on the affair of the succession.

The Hidden Imam, however, will eventually leave his Greater Occultation and appear (zuhur ) to the world of humanity. This return is the most significant event in the future for the Shi'ite faithful and has thunderous eschatological consequences. This return will occur shortly before the Final Judgment and the end of history. Imam Mahdi will return at the head of the forces of righteousness and do battle with the forces of evil in one, final, apocalyptic battle.