Musnad Ahmad 25:483

'Attab ibn Ziyad narrated to us, Abdullah—meaning Ibn al-Mubarak—narrated to us, he said: Musa ibn 'Uqbah informed us, from Muhammad ibn 'Amr ibn 'Ata', that he narrated to him that he heard Ibn 'Abbas saying: "I saw the Messenger of Allah (peace and blessings of Allah be upon him) eat from a shoulder or an arm [of a sheep], then he stood up and prayed, and he did not perform ablution."