The contrasting opinions regarding the succession are primarily based on differing interpretations of events in early Islamic history as well as of "hadiths" (sayings of Muhammad). Sunnis believe that Muhammad had no appointed successor and had instead intended that the Muslim community choose a leader from among themselves. They accept the rule of Abu Bakr, who was elected at Saqifah, and that of his successors, who are together termed the Rashidun Caliphs. Conversely, Shi'ites believe that Ali had previously been nominated by Muhammad as heir, most notably during the Event of Ghadir Khumm. They primarily see the rulers who followed Muhammad as illegitimate, with the only rightful Muslim leaders being Ali and his lineal descendants, the Twelve Imams, who are viewed as divinely appointed.