“There will definitely be a people after me from my nation who recite the Quran yet it will not even reach beyond their throats. They will pass through the religion as an arrow passes through a target, then they will not return back to it. They are the worst of people, the worst of all creatures.”
(Aḥmad, Muslim, and Ibn Mājah)
Thus khawarij are not the people outside of islam but they are the ones who are from inside. They know about islam but their deeds are such that they are excluded from islam. Do they exist now or they don't is a widely asked question. In fact, there are different sects who call each other khawarij. Prophet Muhammad pbuh said about them;
Ibn ‘Umar said, “I heard Allah’s messenger (pbuh) say, ‘Every time a new generation of them rises, they will then disappear,’ more than twenty times and then said: “Until the Anti- Christ finally appears among them.”Ibn Mājah (no. 174 and it is in “Ṣaḥīḥ al-Jāmi’” by al-Albānī (no. 8027)
This hadith tells us that this groups will appear and disappear. We have read form the initial history of islam that such a group was present. And these people fought against the companions of Muhammad pbuh. and their end is such that the anti Christ, the most filthy creature, the biggest fitnah of all fitnah, will appear among them. This means that they will be posing islam and creating fitnah when anti christ will appear among them. History has proven it that fitnah always spreads and nourishes among the crooked and evil minds. In another hadith, prophet Muhammad pbuh called them dogs of hell fire. This shows what kind of threat they pose for muslim ummah. Indeed, any such group who practices islam but remains empty can do only one thing, and that is misleading the common lot. When a person cannot be changed by islam, It only means that he has no share of wisdom due to his haughtiness. And khawarij are the proud, haughty people who do not consider anyone in deen above them, the same as iblees did with adam a.s.
In another hadith, prophet Muhammad pbuh told us about their signs;
Abū Sa’ī d al-Khudrī RA said, “We were with Allah’s messenger ( pbuh ) while he was distributing some wealth. Dhu al-Khuwaṣ irah, a man from the Tamī m tribe, came to him and said, ‘Messenger of Allah, be fair!’ The prophet replied:
“Beware. And who would be fair if I was not? You would be ruined if I were not just.”
‘Umar said, “Messenger of Allah, allow me to strike his neck.” He replied: “Leave him. He will certainly have companions (from his progeny) whom one of you would belittle his own prayer when compared to their prayer and his fasting compared to their fasting. They will recite the Quran but it will not go beyond their
throats. They will pass through the religion as an arrow passes through a game animal. One could then look at the arrowhead and not see a thing remaining on it. He could look at the binding which attaches the arrowhead to the rod and not see a thing. He could look at the rod and not see a thing. He could look at the
feathers and not see a thing. It would go straight through the bowels and blood. Their sign is that of a black man. One of his limbs will appear like a woman’s breast or a disfigured lump of flesh. They will emerge when the people are disunited.” (Bukhari, Mulsim)
This hadith tells us that these people are more practicing than many of the muslims. Their religion ( as appears) is far better than the one who compares himself with them. But still, just like an arrow who goes straight through the flesh of the game with nothing on it, islam goes away from them. It is because of their pride, their over confidence and their looking down upon other. And the last line of the hadith gives us the key. They survive on disunity of the people. That is, they survive on perfect chaos and fitnah. Whoever they are, they use islam for worldly gains.