A Muslim Who Commits a Grave Sin Ceases to Be a Believer

The Kharijite position on grave sin grew directly out of the Battle of Siffin in 657, fought between Ali, the fourth caliph, and Muawiya, the governor of Syria who contested his succession. When Ali agreed to settle the dispute by arbitration rather than continued fighting, a faction within his own army rejected the agreement outright, holding that judgment belonged to God alone and that Ali had sinned gravely by submitting a matter of right rule to human arbitrators. From that founding grievance the group, who took the name Kharijites, those who go out, from their withdrawal from Ali's camp, drew a wider theological conclusion: that grave sin of any kind puts the person who commits it outside the community of belief entirely, stripping a wrongdoer, ruler or otherwise, of any claim to be a believer at all. The Venture of Islam traces how this reasoning made the Kharijite position inseparable from a political one, since a ruler who governed unjustly had, on this account, ceased to be Muslim and so could rightly be resisted and even killed, a conclusion later Kharijite factions carried into repeated armed uprisings against Umayyad governors and, at the doctrine's origin, against Ali himself, whom a Kharijite assassin killed in 661 for having accepted the arbitration the group had condemned.

The Kharijite verdict on grave sin became, in the assessment of historians of Islamic theology, the first great doctrinal question the young Muslim community had to answer, and nearly every subsequent theological school took shape partly in reaction to it. The Murjia answered by refusing the Kharijite claim to judge at all, holding that the true state of a sinner's faith could not be known by other believers and had to be deferred, or postponed, to God's judgment alone, a position whose very name, the postponers, marks it as a direct reply. The Mutazila, working out a more systematic middle position, held that a Muslim who commits a grave sin without repenting occupies neither full belief nor outright unbelief but an intermediate station of its own, a formal category the Encyclopaedia of Islam credits as one of the school's foundational doctrines. The emerging Sunni consensus settled on a third answer, that sin, however grave, does not by itself remove a person from the community of believers, leaving judgment of a sinner's ultimate standing to God in the next life. The Kharijite movement itself splintered further under the pressure of its own logic, producing the extreme Azariqa, who extended the verdict of unbelief even to fellow Muslims who declined to fight alongside them, and the more moderate Ibadis, whose descendants in Oman today explicitly reject the Kharijite label while preserving elements of its early theology.