Musannaf Ibn Abi Shayba 38:125

Abu Bakr narrated to us, he said: Ibn ‘Ulayyah narrated to us, from Ayyub, from Ibn Sirin, from ‘Ubaydah, from ‘Ali, who mentioned the Khawarij. He said: "Among them is a man whose hand is malformed (mukhdaj), or stunted (mu’dan), or withered (mashdud). Were it not that you would become arrogant, I would tell you what Allah has promised those who kill them, upon the tongue of Muhammad, may Allah bless him and grant him peace." I said: "Did you hear it from Muhammad, may Allah bless him and grant him peace?" He said: "Yes, and by the Lord of the Kaaba," [repeating it] three times.