Shama-il Tirmidhi Chapter 026, Hadith Number 002 (177).
Ibn 'Abbaas Radiyallahu 'Anhu relates: "Rasulullah Sallallahu 'Alayhi Wasallam once, after relieving himself in the toilet, came out, and was served food. The Sahaabah inquired: 'Will you not perform wudu?'. Rasulullah Saliallahu 'Alayhi Wasallam replied: 'Do I have to perform salaah, that wudu must be performed?'"
It has been mentioned in the previous hadith, that it is not mustahab to perform wudu before eating. It is better to be in the state of wudu at all times. Physical cleanliness has an effect on spiritual cleanliness. It is therefore recommended that wudhu be performed after visiting the toilet.