Are the Khawarij considered our brethren in faith, and should they be greeted with the Muslim salutation or with the saying: "Peace be upon whoever follows guidance"?

The Khawārij are a misguided sect that differed from thel Ahl al-Sunnah (definition) in fundamental matters, including the excommunication of the perpetrator of major sins and some Companions, and the denial of the vision of Allah in the afterlife and the punishment of stoning. Whoever believes in any of the aforementioned is a Khāriji. Scholars have differed regarding their disbelief, and those who considered them Muslims treated them accordingly. Greeting innovators may be withheld as a deterrent to them, while being cautious not to accuse anyone of this innovation without clear evidence.