Sunan Ibn Majah, Chapter: The Chapters on Food

"The Messenger of Allah (saw) was eating food with six of his Companions when a Bedouin came and ate it all in two bites. The Messenger of Allah (saw) said: 'If he had said Bismillah, it would have sufficed you (all). When any one of you eats food, let him say Bismillah, and if he forgets to say Bismillah at the beginning, let him say Bismillah fi awwalihi wa akhirih (In the Name of Allah at the beginning and at the end).'"