Origins and the Succession Dispute

When Muhammad died in Medina in 632 CE without naming an unambiguous successor, the community's leading men gathered at a hall called Saqifat Bani Sa'ida and chose Abu Bakr, an early companion, as caliph, while Ali ibn Abi Talib and Muhammad's household were still occupied with his burial. Sunni tradition remembers this as a legitimate act of consultation among the believers, the model for the three caliphates that followed under Abu Bakr, Umar and Uthman before Ali himself finally became the fourth caliph. Shia tradition remembers it as a usurpation. In the Shia reading, Muhammad had already designated Ali at Ghadir Khumm, a watering place on the road back from his final pilgrimage, where he is reported to have told the assembled pilgrims that whoever held him as master should hold Ali as master too.

Sunni Islam accepts that the event occurred but reads the words as an expression of closeness and affection, not a formal transfer of religious authority. Ali did eventually become caliph in 656 CE, only to be assassinated five years later by a Kharijite in the mosque at Kufa, and the dispute did not end with him. His son Husayn was killed at Karbala in 680 CE resisting the Umayyad caliph Yazid, an event that gave Shia Islam its central narrative of righteous suffering under unjust worldly power, marked every year at Ashura and still central to how Shia Muslims understand legitimate authority.