Sahih Muslim Book 3, Hadith Number 687.

Chapter : Ablution is essential where one takes something cooked with the help of fire.

‘Abdullah b. Ibrahim b. Qariz reported that he found Abu Huraira performing ablution in the mosque, who said: I am performing ablution because of having eaten pieces of cheese, for I heard the Messenger of Allah (may peace be upon him) say: Perform ablution (after eating anything) touched by fire.