And the way of the Muslims has never ceased upon this (methodology) [of fighting and killing the Khārijites], though they did not declare them (the Khārijites) to be apostates like those whom [Abu Bakr] al-Ṣiddīq (رضي الله عنه)fought against. And this is despite the command of the Messenger of Allāh (صلى الله عليه وسلم) to fight against them, as occurs in the authentic ḥadīths, and also despite what has been reported about them in the ḥadīth of Abū Umāmah, collected by at-Tirmidhī and others that they are "The most evil of those who are killed under the sky and how excellent is the one killed by them." Meaning that they are more harmful to the Muslims than others, for there are none which are more harmful to the Muslims than them, neither the Jews and nor the Christians. For they strived to kill every Muslim who did not agree with their view, declaring the blood of the Muslims, their wealth, and the slaying of their children to be lawful, while making takfīr of them. And they considered this to be worship, due to their ignorance and their innovation that caused to stray...

Ahl al-Sunnah (orthodox Sunnī Muslims) are agreed that they (the Khārijites) are astray innovators, that it is obligatory to fight them on the authority of authentic texts and that from the most virtuous of the actions of the Chief of the Believers, ʿAlī (رضي الله عنه) was fighting against the Khārijites and the Companions concurred (with him) upon fighting them.

The second (view): That they (the Khārijites) are disbelievers, apostates (from Islām), it is permissible to initiate fighting against them, to kill their captives and pursue those who flee, and if they are captured, their repentance is sought and if they do not, they are killed.