Musnad Ahmad 5:424

Abdullah narrated to us, Muhammad ibn Abi Bakr al-Muqaddami narrated to us, Hammad—meaning Ibn Zayd—narrated to us, from Ayyub and Hisham, from Muhammad, from Ubaydah, that Ali mentioned the people of al-Nahrawan and said: "Among them is a man with a deformed hand—or a withered hand, or a stunted 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." I said to Ali: "Did you hear it from him?" He said: "Yes, by the Lord of the Kaaba."