The characteristics of the Khawarij and the ruling on killing them

It is narrated from Sharik bin Shihab; he said: I longed to meet a Companion of the Messenger of Allah (peace and blessings be upon him) who would narrate to me a hadith about the Khawarij. Then I met Sayyiduna Abu Barzah al-Aslami (may Allah be pleased with him) on the day of Arafah, among a group of his companions. I said: O Abu Barzah, tell us something you heard from the Prophet (peace and blessings be upon him) about the Khawarij. He said: I will tell you what my ears heard and my eyes saw: Gold coins (dinars) were brought to the Messenger of Allah (peace and blessings be upon him) from some land, and he (peace and blessings be upon him) was distributing them, when a black man came to him whose hair was shaved (or cut short); he was wearing two white garments, and between his eyes was the mark of prostration. He presented himself before the Messenger of Allah (peace and blessings be upon him): first he came from in front of him, but he (peace and blessings be upon him) gave him nothing; then he came from the left, but he (peace and blessings be upon him) gave him nothing; then he came from behind him and said: By Allah, O Muhammad, you have not been just in the distribution today. The Prophet (peace and blessings be upon him) became angry (on hearing this) and said: "After me you will not find anyone more just than me" (he (peace and blessings be upon him) said this three times). Then he said: "From the direction of the east, people will emerge whose way will be just like this (like this man's); they will recite the Qur'an but it will not go beyond their throats; they will pass out of the religion as an arrow passes right through the game, then they will not return to it (and he (peace and blessings be upon him) placed his hand on his blessed chest). Their sign will be shaving the head. They will keep emerging until their last group emerges (with the Dajjal). So when you see them, kill them (Hammad said that he (peace and blessings be upon him) said this three times). They are the worst of all creation and created beings (Hammad said that he said this three times as well)." And he (peace and blessings be upon him) also said: "They will not return to it (the religion)."
This hadith is sahih (authentic) on the condition of Muslim, but the two Shaykhs (Bukhari and Muslim) did not record it.

It is narrated from Sayyiduna Anas (may Allah be pleased with him) that the Prophet (peace and blessings be upon him) said: "Soon there will be disagreement and division in my Ummah, and people will come who will amaze you (with their devotion) and who will be pleased with themselves. Those who kill them will be closer to Allah than they are. They will speak very well, but their deeds will be very bad; they will call to Allah, but they will have no connection with Allah. So when you find them, put them to eternal sleep (kill them)." The Companions said: O Messenger of Allah, tell us their signs. He (peace and blessings be upon him) said: "Their sign is shaving the head and tasbit," that is, removing the hair from the roots.
This hadith is sahih (authentic) on the condition of the two Shaykhs (Bukhari and Muslim), but they did not record it. Imam al-Awza'i also narrated it from Qatadah, from Anas (may Allah be pleased with him), and it too is sahih (authentic) on the condition of the two Shaykhs.