Musnad Ahmad 1153:2273

'Abd al-Wahhab narrated to us, he said: Hisham—meaning Ibn Abi 'Abd Allah—informed us, from Budayl, from 'Abd Allah ibn 'Ubayd ibn 'Umayr, that a woman among them called Umm Kulthum narrated to him from 'A'ishah, that the Messenger of Allah (may Allah bless him and grant him peace) was eating food with six of his companions. A hungry Bedouin came and ate it in two mouthfuls. He (the Prophet) said: "Had he mentioned the name of Allah, the Mighty and Majestic, it would have sufficed you all. So when one of you eats, let him mention the name of Allah. If he forgets the name of Allah at the beginning of it, let him say: 'In the name of Allah, at its beginning and its end.'"