Maliks Muwatta Book 002, Hadith Number 027.

Section : Discontinuing Doing Wudu on Account of Eating Cooked Food.

It was related to me from Malik from Musa ibn Uqba from Abd ar-Rahman ibn Yazid al-Ansari that when Anas ibn Malik came back from Iraq, Abu Talha and Ubayy ibn Kab visited him. He brought them some cooked food and they ate, and then Anas got up and did wudu. Abu Talha and Ubayy ibn Kab asked, "What's this, Anas? Is it an Iraqi custom?" and Anas said, "I wish I had not done it." (i.e. wudu). Abu Talha and Ubayy ibn Kab both got up and prayed without doing wudu.