Musnad Ahmad 524:1

Yahya ibn Sa'id narrated to us, from Hisham ibn 'Urwah, who said: Al-Zuhri narrated to me, from so-and-so son of 'Amr ibn Umayyah, from his father, who said: "I saw the Prophet, peace and blessings of Allah be upon him, eat meat or a piece of meat, and he did not rinse his mouth, nor did he touch water, and then he prayed."