"Kharijis argued that sins themselves were a form of kufr (disbelief in God). They argued that if you commit a sin, you are in effect a disbeliever in God and thus could be fought and killed, even if you were a Companion of the Prophet ﷺ or a caliph. Furthermore, if you disagreed with their belief that sins are disbelief, you are by default a disbeliever and could be fought and killed."