the earliest Islāmic sect, which traces its beginning to a religio-political controversy over the Caliphate.

After the murder of the third caliph, ʿUthmān, and the succession of ʿAlī (Muḥammad's son-in-law) as the fourth caliph, Muʿāwiyah, the governor of Syria, sought to avenge the murder of ʿUthmān. After fighting the indecisive Battle of Ṣiffīn (July 657) against Muʿāwiyah's forces, Alīʿ was forced to agree to arbitration by umpires. This concession aroused the anger of a large group of ʿAlī's followers, who protested that “judgment belongs to God alone” ( Qurʾān 6:57) and believed that arbitration would be a repudiation of the Qurʾānic dictum “If one party rebels against the other, fight against that which rebels” (49:9). A small number of these pietists withdrew (kharajū) to the village of Ḥarūrāʾ under the leadership of Ibn Wahb and, when arbitration proved disastrous to ʿAlī, were joined near Nahrawān by a larger group.

These Khārijites, as they came to be known, were opposed equally to ʿAlī's claims and to those of Muʿāwiyah (Muʿāwiyah I). Repudiating not only the existing caliphal candidates but all Muslims who did not accept their views, the Khārijites engaged in campaigns of harassment and terror. In the Battle of Nahrawān (July 658) Ibn Wahb and most of his followers were killed by ʿAlī, but the Khārijite movement persisted in a series of uprisings that plagued both ʿAlī (whom they assassinated) and Muʿāwiyah (who succeeded ʿAlī as caliph). In the period of civil war (fitnah) following the death of the caliph Yazīd I (683), the Khārijites were the source of serious disruptions within the Umayyad domain and in Arabia. Subdued through the intensive campaigning of al-Ḥajjāj, the Khārijites did not stir again until the collapse of the Umayyads, and then their two major rebellions, in Iraq and Arabia, ended in defeat.

The Khārijites' constant harassment of the various Muslim governments was less a matter of personal enmity than a practical exercise of their religious beliefs. They held that the judgment of God could only be expressed through the free choice of the entire Muslim community. They insisted that anyone, even a black slave, could be elected caliph (that is, head of the Muslim community) if he possessed the necessary qualifications, chiefly religious piety and moral purity. A caliph may be deposed upon the commission of any major sin. The Khārijites thus set themselves against the legitimist claims (to the Caliphate) of the tribe of Quraysh (among the Sunnites) and of ʿAlī's descendants (among the Shīʿites). As proponents of the democratic principle, the Khārijites drew to themselves many who were dissatisfied with the existing political and religious authorities.

Besides their democratic theory of the Caliphate, the Khārijites were known for their puritanism and fanaticism. Any Muslim who committed a major sin was considered an apostate. Luxury, music, games, and concubinage without the consent of wives were forbidden. Intermarriage and relations with other Muslims were strongly discouraged. The doctrine of justification by faith without works was rejected, and literal interpretation of the Qurʾān was insisted upon.

Within the Khārijite movement the Azāriqah of Basra were the most extreme subsect, separating themselves from the Muslim community and declaring death to all sinners and their families. The more moderate subsect of the Ibāḍīyah, however, survived into the 20th century in North Africa, Oman, and Zanzibar, with about 500,000 members.