Musnad Ahmad 789:20

'Affan narrated to us, Hammad bin Salamah narrated to us, Al-Azraq bin Qays informed us, from Sharik bin Shihab, who said: I used to wish to meet a man from the companions of the Prophet, may Allah bless him and grant him peace, who would tell me about the Khawarij. So I met Abu Barzah on the day of Arafah among a group of his companions, and I said: "O Abu Barzah, tell us something you heard the Messenger of Allah, may Allah bless him and grant him peace, say regarding the Khawarij." He said: "I will tell you what my ears heard and my eyes saw. Gold coins were brought to the Messenger of Allah, may Allah bless him and grant him peace, and he was distributing them. With him was a black man with cropped hair, wearing two white garments, and between his eyes was the mark of prostration. He confronted the Messenger of Allah, may Allah bless him and grant him peace, coming at him from the front, but he did not give him anything. Then he came at him from behind, but he did not give him anything. He said: 'By Allah, O Muhammad, you have not been just in the distribution today.' The Messenger of Allah, may Allah bless him and grant him peace, became intensely angry, then said: 'By Allah, you will not find anyone after me who is more just to you than I am.' He said it three times. Then he said: 'There will emerge from the direction of the east men, as if this one is among them. Their guidance is like this; they recite the Quran, but it does not pass beyond their collarbones. They pass through the religion just as an arrow passes through the game; they will not return to it'—and he placed his hand on his chest—'their sign is shaving. They will continue to emerge until the last of them emerges. So if you see them, kill them.' He said it three times. 'They are the worst of creation and the creatures.' He said it three times." Hammad said: "They will not return to it."