Musnad Ahmad 903:9

Muhammad ibn Ja‘far narrated to us, Shu‘bah narrated to us, from ‘Asim al-Ahwal, who said: I heard ‘Abdullah ibn Sarjis say: I came to the Messenger of Allah (peace and blessings of Allah be upon him) and ate some of his food with him. I said: "May Allah forgive you, O Messenger of Allah." I then said: "Shall I seek forgiveness for you?" Shu‘bah said: "Or a man said to him." He said: "Yes, and for you." And he recited: {And ask forgiveness for your sin and for the believing men and believing women} [Muhammad: 19]. Then I looked at the prominence of his right shoulder, or his left shoulder—Shu‘bah is the one who is uncertain—and it was like the appearance of a cluster of warts upon it.