Musannaf Ibn Abi Shayba 3:5543

Abu Usama narrated to us, from Hisham ibn Urwa, from a son of Abu al-Malih, from his father, who said: We were with Abu Bakr, and he had gone out for the Maghrib prayer, and the mu'adhdhin had given the adhan. A bowl containing tharid and meat was brought to him. He said: "Sit and eat, for the food was only made to be eaten." So he ate. Then he called for water, washed his fingertips, rinsed his mouth, and prayed.