Musnad Abu Ya'la al-Mawsili 3:219

Ubayd Allah ibn Umar narrated to us, Khalid ibn al-Harith narrated to us, Ibn Awn narrated to us, from Muhammad, from Ubaydah, that he said: "I will not narrate to you except what I heard from him"—meaning Ali. He said: "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 said: "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," three times. "Among them is a man who is *mukhdaj* (deformed) or *muthdan* (having a breast-like protrusion) of the hand." He said: "I think he said, or *muwdan* of the hand." He said: "So they searched for that man and found him, from here and from here, like a woman’s breast, with hairs upon it." Muhammad said: "And Ubaydah swore to me three times that he heard it from Ali, and Ali swore three times that he heard it from the Messenger of Allah, may Allah bless him and grant him peace."