Maliks Muwatta Book 2, Hadith Number 26.
Section : Discontinuing Doing Wudu on Account of Eating Cooked Food.
Yahya related to me from Malik from Muhammad ibn al-Munkadir that the Messenger of Allah, may Allah bless him and grant him peace, was invited to eat, and some bread and meat was brought to him. He ate some of it, and then did wudu and prayed. Then more of the same food was brought and he ate some more and then prayed without doing wudu.