Musannaf Ibn Abi Shayba 38:136

Qatan ibn Abd Allah Abu Marra narrated to us, from Abu Ghalib, who said: I was in the mosque of Damascus, and they brought seventy heads of the Haruriyya. They were set up on the steps of the mosque. Abu Umama came and looked at them, then said: "Dogs of Hell, the worst of the slain who were killed under the shadow of the sky, and the best of those who were killed are those whom they killed under the sky." Then he wept. He looked at me and said: "O Abu Ghalib, you are from the land of these people?" I said: "Yes." He said: "May Allah protect you from them." I think he said: "May Allah protect you from them." He said: "Do you recite Al-Imran?" I said: "Yes." He said: "[It is He who has sent down to you, [O Muhammad], the Book; in it are verses [that are] precise - they are the foundation of the Book - and others unspecific. As for those in whose hearts is deviation [from truth], they will follow that of it which is unspecific, seeking discord and seeking an interpretation [suitable to them]. And no one knows its [true] interpretation except Allah. But those firm in knowledge...]" He said: "[On the Day [some] faces will turn white and [some] faces will turn black. As for those whose faces will turn black, [to them it will be said], 'Did you disbelieve after your belief? Then taste the punishment for what you used to reject.']" I said: "O Abu Umama, I saw you shedding your tears." He said: "Yes, out of mercy for them, for they were of the people of Islam." He said: "The Children of Israel split into seventy-one sects, and this nation will increase by one sect; all of them are in the Fire except the Great Majority. Upon them is what they were burdened with, and upon you is what you were burdened with. If you obey him, you will be guided. The Messenger is not responsible except for clear notification. Hearing and obeying is better than division and disobedience." A man said to him: "O Abu Umama, is this your own opinion, or something you heard from the Messenger of Allah, may Allah bless him and grant him peace?" He said: "I would be very bold if that were the case. Rather, I heard it from the Messenger of Allah, may Allah bless him and grant him peace, not once, nor twice," until he mentioned seven times.