Shia

The Shi'a constitute 10–20% of Islam and are its second-largest branch. While Sunnis believe that Muhammad did not appoint a successor, Shias believe that during The Farewell Pilgrimage the prophet appointed his son-in-law, Ali ibn Abi Talib, as his successor as shown by the Hadith of the pond of Khumm. As a result, they believe that Ali ibn Abi Talib was the first Imam (leader), rejecting the legitimacy of the previous Muslim caliphs since they were not appointed by the prophet. Shias believe that the political and religious leadership of Imams come from the direct descendants of Muhammad and Ali, also known as the Ahl al-Bayt. To most Shias, an Imam rules by right of divine appointment and holds "absolute spiritual authority" among Muslims, having final say in matters of doctrine and revelation. However, the Imams are not allowed to introduce new laws or eradicate old ones; they are simply required to interpret and reflect the will of Allah and the prophet.

Shia Islam has several branches, the largest of which is the Twelvers, followed by Zaidis and Ismailis. The Twelvers believe that there were 12 Imams or caliphs after the Prophet. They often cite the Hadith of the Twelve Successors as evidence. Shias prefer hadiths attributed to the Ahlul Bayt and close associates. The Twelver Shi'a follow a legal tradition called Ja'fari jurisprudence. Other smaller groups, include the Bohra, and Druze, as well as the Alawites and Alevi. Branches of Shia Islam which deviate from mainstream Shia doctrine are described by orthodox Shias as Ghulat.