The prophetic narrations regarding the khawarij, relate that they would thrust their self away from the religion of Islam.
Narrated ‘Ali: I relate the traditions of Allah’s Apostle to you for I would rather fall from the sky than attribute something to him falsely. But when I tell you a thing which is between you and me, then no doubt, war is guile. I heard Allah’s Apostle saying, “In the last days of this world there will appear some young foolish people who will use (in their claim) the best speech of all people (i.e. the Qur’an) and they will abandon Islam as an arrow going through the game. Their belief will not go beyond their throats (i.e. they will have practically no belief), so wherever you meet them, kill them, for he who kills them shall get a reward on the Day of Resurrection.” [Sahih Bukhari, Book 56 Hadith 808]
This leaving the religion, according to Ibn Taymiyya, was due to their branding of Muslims as being non-Muslims: “Since they were armed and inclined to fight, their opposition to the community manifested when they started killing the people. However, as for today, most people [due to their religious garb and appearance] do not know of them…… [A]nd their ‘passing through the religion’ is their leaving it because of having declared lawful the blood and wealth of Muslims.” [Ibn Taymiyya, al-Nubuwwat, p.222]
Ibn Taymiyya elsewhere also confirms the emergence of the Khawarij movement during the end times: “And these Kharjites are not only the armed group that was known in history [during the caliphate of ‘Ali]; rather, they are the ones who will appear time and time again until the time of the al-Dajjal. The Prophet’s particular mention of the group that appeared during the time of ‘Ali b. Abi Talib was due to the many traits found in them. Anyone in whom these traits are found is counted amongst them, for the particular mention of them [by the Prophet (peace be upon him)] was not because the ruling applied to them alone, but rather it was because those who were addressed during the Prophet’s time needed to fix the identity in the times to come.” [Ibn Taymiyya, Majmua al-fatawa, 28:495-496]