Sahih Bukhari Volume 7, Book 70, Hadith 5378

حَدَّثَنَا عَلِيُّ بْنُ عَبْدِ اللَّهِ، أَخْبَرَنَا سُفْيَانُ، قَالَ الْوَلِيدُ بْنُ كَثِيرٍ أَخْبَرَنِي أَنَّهُ، سَمِعَ وَهْبَ بْنَ كَيْسَانَ، أَنَّهُ سَمِعَ عُمَرَ بْنَ أَبِي سَلَمَةَ، يَقُولُ كُنْتُ غُلاَمًا فِي حَجْرِ رَسُولِ اللَّهِ صلى الله عليه وسلم وَكَانَتْ يَدِي تَطِيشُ فِي الصَّحْفَةِ فَقَالَ لِي رَسُولُ اللَّهِ صلى الله عليه وسلم ‏"‏ يَا غُلاَمُ سَمِّ اللَّهَ، وَكُلْ بِيَمِينِكَ وَكُلْ مِمَّا يَلِيكَ ‏"‏‏.‏ فَمَا زَالَتْ تِلْكَ طِعْمَتِي بَعْدُ‏.

Narrated By 'Umar bin Abi Salama : I was a boy under the care of Allah's Apostle and my hand used to go around the dish while I was eating. So Allah's Apostle said to me, 'O boy! Mention the Name of Allah and eat with your right hand, and eat of the dish what is nearer to you." Since then I have applied those instructions when eating.