Shiite Muslim This branch of Islam, constituting some 15% of Muslims, holds that the Prophet Muhammad designated his cousin Ali and his descendants as his successors. They thus differ from the majority Sunni branch, which holds that the Prophet did not name a successor. Shiites are close in doctrine to Sunni Muslims, but Shiites, because of their long-time minority status, tend to differentiate sacred from secular authority more than Sunnis do. They also regard Ali's successors, the Imams, to have been infallible transmitters of spiritual authority. Since the line of Imams ceased in 941 A.D., religious authority has been vested in jurists known as mujtahid. Shiites constitute a majority of Muslims in Iran and parts of Iraq.