Zayd, a half-brother of Muhammad al-Baqir, also asserted a claim to imamate on the basis that the title can belong to any descendant of Hasan or Husayn who is learned, pious, and revolts against the tyrants of his time. On this basis, his followers, known as Zaydis, consider Zayd as the rightful successor of the fourth Shia Imam, though the fourth Imam himself did not revolt against the Umayyads and instead adopted a policy of quiescence. Initially, Zayd's activist approach gained him a large following. However, as he increasingly compromised with the traditionalists, some of Zayd's supporters are said to have returned to Muhammad al-Baqir. According to Jafri, a related incident is when two Kufan Shias asked Zayd if the first Shia Imam, Ali, was an Imam before he resorted to the sword. When Zayd refused to answer this question, the two broke their allegiance with him and went back to Muhammad al-Baqir. Eventually, Zayd took up arms against the Umayyads in 122 AH and was killed in Kufa by the forces of Caliph Hisham. One faction of the Zaidiyyah, called the Batriyya, attempted a compromise between Sunni and Shia by accepting the legitimacy of the Sunni caliphs while maintaining that they were inferior to Ali. Imamat al-Mafdul (literally, "imamate of the inferior") is the belief that, while Ali was better suited to succeed Muhammad, the reigns of Abu Bakr and Umar must be acknowledged since Ali did not revolt against them. Ibadi The Ibadi, an Islamic school distinct from Sunni and Shia, believe that leadership of the Muslim community is not something which should be decided by lineage, tribal affiliations or divine selection, but rather through election by leading Muslims. They do not view their leaders as infallible. In particular, if a leader fails to maintain a legitimate government in accordance with the Islamic law, it is the duty of the population to remove him from power. The Rashidun Caliphs are seen as rulers who were elected in a legitimate fashion and, in particular, Abu Bakr and Umar are viewed as righteous leaders. However, Uthman is viewed as having committed grave sins during the latter half of his rule and was deserving of death. Ali is also similarly understood to have lost his mandate. The Ibadi have been labeled by some scholars as the "moderate Kharijites." Their first Imam was Abd Allah ibn Wahb al-Rasibi, who led the Kharijites