Musnad Ahmad 5:418

'Abdullah narrated to us, 'Ubaydullah ibn 'Umar al-Qawariri narrated to me, Hammad ibn Zayd narrated to us, Ayyub informed us, from Muhammad, from 'Ubaydah, who said: 'Ali mentioned the people of al-Nahrawan and said: "Among them is a man with a deformed hand—or a withered hand, or a truncated hand. Were it not that you would become arrogant, I would have informed you of what Allah has promised those who kill them, upon the tongue of Muhammad, may Allah bless him and grant him peace." He (the narrator) said: I said, "Did you hear it from him?" He said, "Yes, by the Lord of the Ka'bah."