Maliks Muwatta Book 49, Hadith Number 32.
Section : General Section on Food and Drink.
Yahya related to me from Malik from Abu Nuaym that Wahb ibn Kaysan said, “The Messenger of Allah, may Allah bless him and grant him peace, was brought food while his stepson Umar ibn Salama was with him. The Messenger of Allah, may Allah bless him and grant him peace, said to him, ‘Say “Bismillah,” and eat what is in front of you.'”