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."
English reference: Vol. 1, Book 1, Hadith 132
Arabic reference: Book 1, Hadith 133