Musnad Abu Ya'la al-Mawsili 79:3

Abu Ubaydah ibn al-Fudayl ibn Iyad narrated to us, Abu Sa’id, the freed slave of Banu Hashim, narrated to us, al-Mas’udi narrated to us, from ‘Awn ibn ‘Abd Allah, who said: I met an old man in al-Sham and I said, "Did you hear anything from the Messenger of Allah, may Allah bless him and grant him peace?" He said, "Yes, I heard him saying: 'O Allah, forgive us and have mercy upon us.'"