Musnad Abu Ya'la al-Mawsili 80:1

Ibrahim ibn al-Hajjaj al-Sami narrated to us, Abd al-Wahid ibn Ziyad narrated to us, Asim al-Ahwal narrated to us, from Abdullah ibn Sarjis, who said: I saw the Messenger of Allah (may Allah bless him and grant him peace), and I ate bread and meat—or he said: tharid—with him. I said, "May Allah forgive you, O Messenger of Allah." He said, "And you." I said to Abdullah ibn Sarjis, "Did the Messenger of Allah (may Allah bless him and grant him peace) ask for forgiveness for you?" He said, "Yes, and for you." Then he recited this verse: "And ask forgiveness for your sin and for the believing men and believing women" (Muhammad: 19). Then he said: Then I went around until I was behind him, and I saw the Seal of Prophethood at the top of his left shoulder, a collection of moles upon it.