Sahih Bukhari Volume 007, Book 065, Hadith Number 290.

Narrated By Wahb bin Kaisan Abi Nu'aim : A meal was brought to Allah's Apostle while his step-son, 'Umar bin Abi Salama was with him. Allah's Apostle said to him, "Mention the Name of Allah and eat of the dish what is nearer to you."