Shama-il Tirmidhi Chapter 026, Hadith Number 003 (178).
Salmaan Faarisi Radiyallahu 'Anhu says: "I have read in-the Tauraah, that performing wudu (washing the hands) after eating increases blessings. I mentioned this to Rasulullah Sallailahu 'Alayhi Wasallam. Rasulullah Sallallahu 'Alayhi Wasallam said: "Wudu before and after eating (washing the hands and mouth) increases blessings."
It may be possible that only the time (after eating) is mentioned in the Tauraah. In this manner the other time (before eating) was added to the shari'ah of Muhammad Sallailahu 'Alayhi Wasallam. Many laws have been revealed that were not in the shari'ah of the previous ambiyaa. It is possible that both times are mentioned in the Tauraah, and since changes have been made to it, the law of washing the hands before eating, may have been removed from it. The 'ulama have stated that by 'Barakah (blessings) in washing the hands before eating', means increase in the food, and filling of the stomach. The 'Barakah of washing the hands after eating', means that the benefits and intention of eating is fulfilled. i.e. It becomes part of the body, creates energy and stamina, assists in strengthening one to perform 'ibaadah, and to possess good manners.