Sahih Muslim Book 3, Hadith Number 726.

Chapter : It is permissible to eat without ablution and there is no abhorrence in it and performing of ablution immediately (after that) is not essential.

Ibn ‘Abbas reported: We were with the Apostle of Allah (may peace be upon him) and he had come out of the privy. Food was presented to him. It was said to him (by the Companions around him): Wouldn’t you perform ablution? Upon this he said: Why, am I to say prayer that I should perform ablution?