Muhammad began preaching Islam at Mecca before migrating to Medina, from where he united the tribes of Arabia into a singular Arab Muslim religious polity. With Muhammad's death in 632, disagreement broke out over who would succeed him as leader of the Muslim community. While Ali ibn Abi Talib, his cousin and son-in-law, and the rest of Muhammad's close family were washing his body for burial, the tribal leaders of Mecca and Medina held a secret gathering at Saqifah to decide who would succeed Muhammad as head of the Muslim state, disregarding what the earliest Muslims, the Muhajirun, regarded as Muhammad's appointment of Ali as his successor at Ghadir Khumm.