Shama-il Tirmidhi Chapter 026, Hadith Number 001 (176).
Ibn'Abbaas Radiyallahu'Anhu says: "Once when Rasulullah Sallailahu 'Alayhi Wasallam came out of the toilet, after relieving himself from the call of nature, food was served to him. They asked if water for wudu should be brought? He replied: 'I have been commanded to perform wudu when 1 perform salaah'".
Technical wudu is only waajib for salaah. It is not necessary to perform wudu before eating or immediately after relieving one's self. Sayyidina Rasulullah Sallallahu 'Alayhi Wasallam did not perform wudu for it must not be thought that wudu is compulsory after visiting the toilet.