Sunan an Nasai
132
Sahih+2

It was narrated from Ibn 'Abbas that the Messenger of Allah (ﷺ) came out from the toilet and food was brought to him. They said:"Shall we not bring water for Wudu'?" He said: "I have only been commanded to perform Wudu' when I want to pray

SahihAbu Ghuddah
SahihAl-Albani