I would like to ask about the Kharijites?

The Khawarij are a deviant, renegade sect, and this has been established by text and scholarly consensus. It has been stated in the Hadith that they "pass through Islam as an arrow passes through its target" and that they are "the dogs of Hell."

Scholars have differed regarding declaring them disbelievers. The correct view is that they are not declared disbelievers due to their innovation; rather, they are among the people of innovation who have deviated from the methodology of the Ahl al-Sunnah wal-Jama'ah (People of the Sunnah and the Community). Ali ibn Abi Talib and other Companions did not declare them disbelievers; rather, he fought them to repel their injustice and transgression, not because they were disbelievers.

Among the innovations of the Khawarij are: they believe that faith neither increases nor decreases, they declare one a disbeliever for abandoning an obligation, they declare one a disbeliever for committing a major sin, and they revolt with the sword against their Muslim opponents.