Jamiat Tirmidhi: Hadith 3162

"Abu Umamah saw heads (of the Khawarij) hanging on the streets of Damascus. He said: 'The dogs of the Fire and the worst dead people under the canopy of the heavens. The best dead men are those whom these have killed.' He then recited: On the Day when some faces will become white and some faces will become black... (3:106) until the end of the Ayah. I said to Abu Umamah: 'Did you hear it from the Messenger of Allah (ﷺ)?' He said: 'If I had not heard it but one time, or two times, or three times, or four times - until he reached seven - I would not have narrated it to you.'"