Musnad Ahmad 25:686

'Affan narrated to us, Wuhaib narrated to us, Hisham ibn 'Urwah narrated to us, from Wahb ibn Kaysan, from Muhammad ibn 'Amr ibn 'Ata', from 'Abdullah ibn 'Abbas, who said: "I saw the Messenger of Allah, peace and blessings of Allah be upon him, eating a shoulder of a sheep, then he prayed and did not rinse his mouth, and did not touch water."