It is narrated from Sayyiduna Abu Hurayrah (may Allah be pleased with him): I went out with the Messenger of Allah (peace and blessings be upon him), carrying a vessel, and I found him (peace and blessings be upon him) intending to relieve himself.
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الطهارة / 525