He states in Al-Ifṣāḥ: “The scholars concur that when the army of justice destroys the property of the rebels, no liability is incurred, and the same applies to what the rebels destroy.”

If two groups of Muslims fight one another and neither is acting under the imam’s command, but rather out of tribal zeal or a quest for leadership, then both are in the wrong, for each is aggressing against the other with no distinction between them. Accordingly, each party must make good the losses it inflicts upon the other. If, however, one of the two is fighting by order of the imam, that party is in the right and the other is the rebel, as explained earlier.

Should a people espouse the doctrine of the Khawarij—such as declaring those who commit major sins to be unbelievers, deeming the blood of Muslims lawful, and reviling the Companions—they are classified as Khawarij: rebels and flagrant sinners. If, in addition to those views, they rise up against the authority of the Muslim imam, it becomes obligatory to fight them.

Shaykh al-Islam Ibn Taymiyyah said concerning the Khawarij: “The people of the Sunnah are agreed that they are innovators and that, on the basis of sound texts, fighting them is obligatory. Indeed, the Companions unanimously fought them. There is no disagreement among Sunni scholars that they are to be fought alongside just rulers. As for fighting under unjust rulers, some of the scholars transmit that it is still permissible—likewise for treaty-breakers from among the People of the Covenant—and this is the majority view. They say: one may go on campaign with any commander, righteous or corrupt, provided the war he wages is lawful. If he fights unbelievers, apostates, treaty-breakers, or the Khawarij in a legitimate battle, one fights with him; but if the battle is illegitimate, one does not.” End of his words.