The majority of both Sunnis and Shi’as share the core beliefs of Islam—the oneness of God and the prophethood of Muhammad—and adhere to the Five Pillars.
The main differences between them today are their sources of knowledge and religious leadership. In addition to the Qur’an and hadith, the Shias and the many sects that comprise them rely on the rulings of their Imams and resulting variations in beliefs and practices.
Historically, the difference originated from the question of succession after the death of the Prophet Muhammad and is related to differing views about appropriate leadership for the Muslim community. Shi’as believe that succession to the spiritual and political rule of the Muslim community lies only with the family and certain descendants of the Prophet Muhammad. Sunnis believe that the Muslim community was free to choose the most qualified person as ruler. Shi’as believe that God chose Muhammad’s cousin Ali, who was married to his daughter Fatima, to be the Prophet Muhammad’s successor, and that Muhammad formally announced this before his death. Shi’as also view Ali as the first in a line of Imams, or preeminent religious leaders, whom they regard as the spiritual and political successors to Muhammad. In contrast, Sunnis believe that Muhammad did not appoint any particular person as his spiritual or political successor.