Musnad Ahmad 757:1

Makki—meaning Ibn Ibrahim—narrated to us, al-Ja'id narrated to us, from al-Hasan ibn 'Abd Allah ibn 'Ubayd Allah, that 'Amr ibn 'Ubayd Allah narrated to him, that he said: "I saw the Messenger of Allah (may Allah bless him and grant him peace) eat a shoulder [of meat], then he stood up and rinsed his mouth, then he prayed and did not perform ablution."