Shia Islam is based on Muhammad's hadith (Ghadir Khumm). Shia consider Ali to have been divinely appointed as the successor to Muhammad, and as the first Imam. The Shia also extend this Imammah to Muhammad's family, the "Ahl al-Bayt" ("the people/family of the House"), and some individuals among his descendants, known as "Imams", who they believe possess special spiritual and political authority over the community, infallibility and other divinely ordained traits. Although there are many Shia subsects, modern Shia Islam has been divided into two main groupings: Twelvers and Ismailis, with Twelver Shia being the largest and most influential group among Shia.