It is narrated from Sayyiduna Ibn Abbas (may Allah be pleased with them both) that the Messenger of Allah (peace and blessings be upon him) came out of the toilet and food was presented to him (peace and blessings be upon him). The people said: Shall we not bring you water for ablution? He (peace and blessings be upon him) said: "I have only been commanded to perform ablution when I stand for the prayer."
Hadith Referenceالمعجم الكبير للطبراني / باب العين / 11195