Ash-Shama'il Al-Muhammadiyah, Book 27, Hadith 181 (English)

Umar bin Abi Salamah Radiyallahu 'Anbu came to Rasululah Sallallahu 'Alayhi Wasallam while food had been served to him. Rasulullah Saliallahu 'Alayhi Wasallam said: "O my Son come near, recite Bismillah, and eat with your right hand from that portion which is in front of you".

حَدَّثَنَا عَبْدُ اللهِ بْنُ الصَّبَّاحِ الْهَاشِمِيُّ الْبَصْرِيُّ، قَالَ‏:‏ حَدَّثَنَا عَبْدُ الأَعْلَى، عَنْ مَعْمَرٍ، عَنْ هِشَامِ بْنِ عُرْوَةَ، عَنْ أَبِيهِ، عَنْ عُمَرَ بْنِ أَبِي سَلَمَةَ، أَنَّهُ دَخَلَ عَلَى رَسُولِ اللهِ صلى الله عليه وسلم، وَعِنْدَهُ طَعَامٌ، فَقَالَ‏:‏ ادْنُ يَا بُنَيَّ، فَسَمِّ اللَّهَ تَعَالَى، وَكُلْ بِيَمِينِكَ، وَكُلْ مِمَّا يَلِيكَ‏.‏

also referenced under: Book 28, Hadith 190 (In-Book)