Shaikh Rabee Bin Haadi (may Allaah preserve him) said:

By Allaah! The Ummah will not be removed from its problems and the (state of) humiliation and degradation they are living in except by returning to the Book of Allaah, the Sunnah Messenger and the understanding of the pious predecessors, (in dealing) with the affair of the Khawaarij and other than them. (Imaam) Al-Aajuriy said: The scholars—past and present—do not differ (with regards to the fact) that the khawaarij are an evil people, disobedient to Allaah and His Messenger, even if they pray, fast and strive in acts of worship.

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[الذريعة إلى بيان مقاصد كتاب الشريعة Vol 1. Page:97]