Shi'a Muslims believe that Muhammad's family (the Imams) were the best source of knowledge about the Qur'an, Islam, and Emulation (the best-qualified teachers of Islam after Muhammad), and the most trusted carriers and protectors of Muhammad's Sunnah (traditions) due to many emphasized sayings by him. Ali was Muhammad's cousin, son-in-law, father of his only descendants and the male head of the Ahlul Bayt (people of the house). After Muhammad's passing, Ali claimed succession in religious and political authority, supported by his family and followers. Shi`ahs believe that by Muhammad's direct order he appointed him successor on many occasions, that he was the rightful leader of the Muslims after Muhammad's passing, and that to follow Muhammad's true Sunnah one must support Ali's successorship.
Shi'as refuse to accept the rule of the initial three Sunni caliphs who proclaimed leadership after Muhammad's passing, believing them illegitimate and inferior to Muhammad's family in all respects. The caliphs are followed by Sunni Muslims, who believe Muhammad did not choose a successor, and that the caliphs were elected according to what they consider Muhammad's instruction of consultation (Shura). Thus they reject what they called dynastic rights to religious authority that Shi`ahs attribute to Muhammad's family. The first caliph, Abu Bakr was chosen after Muhammad's passing at a meeting he had at the saqifah with Umar, another companion of Muhammad. This claim to succession was disputed by `Ali, the Banu Hashim whom he headed, and many other supporters.