The Iranian branch of Islam is known as Shia, which is a four-letter word. Shia is one of the two main branches of Islam, the other being Sunni. Shia Muslims believe that the Prophet Muhammad's descendants should have inherited the leadership of the Islamic community after his death. This belief is based on the teachings of the Quran and the Hadith, which are the sayings and actions of the Prophet Muhammad. Shia Muslims also believe in the concept of Imamah, which is the spiritual and political leadership of the Islamic community by an infallible leader.