Musnad Abu Ya'la al-Mawsili 3:77

'Ubayd Allah ibn 'Umar narrated to us, Hammad ibn Zayd narrated to us, from Ayyub, from Muhammad, from 'Ubaydah, who said: 'Ali mentioned the people of al-Nahrawan, and he said regarding them: "A man with a deformed hand—or a withered hand—is among them. Were it not that you would become arrogant, I would inform 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."