Musnad Ahmad 524:2

Abu Kamil narrated to us, Ibrahim bin Sa'd narrated to us, Ibn Shihab narrated to us, from Ja'far bin 'Amr bin Umayyah al-Damri, from his father: That he saw the Prophet, peace and blessings of Allah be upon him, eating from a shoulder [of a sheep], cutting from it. Then he was called to the prayer, so he prayed and did not perform ablution.