Shaikhul Islaam Ibn Taymiyyah (rahimahullaah) said:

And likewise the khawaarij are a people of the sword and fighting. Their opposition to the Jamaa’ah became clear when they fought the people.  As for today many of the people do not know them (i.e. due to their characteristics being different etc).

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[An-Nubuwwaat 1/139]