The Sunni branch, claiming approximately 90% of all Muslims, argued that the Caliph should belong to Muhammad's tribe, the Qurayah, and that the community should choose him by the process of consensus (ijma). Since Muhammad was the ''Seal of the Prophets,'' the Sunnis considered the responsibilities of the Caliph merely to guard--not continue--the prophetic legacy, and to provide ''for the administration of community affairs in obedience to the Qur'an and prophetic precedent'' (Kerr, 1982, p. 330). Within thirty years of Muhammad's death, four Caliphs were appointed in succession: Abu Bakr (632-634), `Umar (634-644), `Uthman (644-656), and `Ali (656-661). Sunnis regard these first Islamic leaders as ''the four rightly-guided Caliphs,'' since they lived so close to Muhammad. Because of their chronological proximity to Muhammad, Sunnis believe that the sunna (behavior or practice) of these four Caliphs, together with the Prophet's, is authoritative for all Muslims. The Sunnis derive their name from this emphasis on the sunna. While there are subdivisions of this group, distinguished by specific points of interpretation, they all call themselves Sunni.
Garry K. Brantley A Christian Approach to Islam, Apologetics Press, Jan. 1996