Sunan An-Nasai, Chapter: The Book of Purification

that when the Prophet (saw) would go away (to relieve himself) he would go far away. He went to relieve himself when he was on one of his journeys, and said: "Bring me (water for) Wudu." So I brought him (water for) Wudu, and he performed Wudu and wiped over his Khuffs. (Sahih) The Shaikh said: Ismail (one of the narrators) is Ibn Jafar bin Abi Kathir Al-Qari;