Muwatta Malik 1703

وَحَدَّثَنِي عَنْ مَالِكٍ، عَنْ أَبِي نُعَيْمٍ، وَهْبِ بْنِ كَيْسَانَ قَالَ أُتِيَ رَسُولُ اللَّهِ صلى الله عليه وسلم بِطَعَامٍ وَمَعَهُ رَبِيبُهُ عُمَرُ بْنُ أَبِي سَلَمَةَ فَقَالَ لَهُ رَسُولُ اللَّهِ صلى الله عليه وسلم ‏ "‏ سَمِّ اللَّهَ وَكُلْ مِمَّا يَلِيكَ ‏"‏ ‏.‏

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

Reference

Muwatta Malik 1703

In-book

Book 49, Hadith 33