It is narrated from Abdullah bin 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 before him (peace and blessings be upon him). The Companions (may Allah be pleased with them) said: "Shall we not bring you water?" He (peace and blessings be upon him) said: "I have been ordered to perform ablution only when I intend to pray."
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الطهارة / 190