Muhammad died in 632 without a son and, on the Sunni account, without naming a successor. While his household prepared the burial, an assembly of Medinan and Meccan leaders met at the portico of the Banu Saida and acclaimed Abu Bakr as khalifa, successor or deputy, a title that carried no prophetic authority. Umar followed in 634, Uthman in 644 and Ali, the Prophet's cousin and son in law, in 656. Three of the four were murdered.
The disagreement about whether this was the right sequence is the origin of the Sunni and Shia division. Shia tradition holds that Muhammad had designated Ali, most explicitly at Ghadir Khumm, and that the community set the designation aside. Wilferd Madelung's study argues, from the Sunni sources themselves, that the case for Ali's claim was considerably stronger than the later Sunni consensus allowed, and that the early caliphate is better read as a contested political settlement than as a smooth succession.
Uthman's reign produced the single most consequential act of the period, the establishment of an authoritative written text of the Quran and the withdrawal of competing copies, and also the grievances, over governorships given to his kinsmen, that led to his murder in 656. The first fitna followed, Ali against the Prophet's widow Aisha at the Battle of the Camel and then against Muawiya at Siffin, where arbitration split off the Kharijites, one of whom killed Ali in 661.