Sunan Abi Da'ud

Narrated Anas b. Malik : The Apostle of Allaah ( sal Allaahu alayhi wa sallam ) entered a park. He was accompanied by a boy who had a jug of water with him. He was the youngest of us. He placed it near the lote-tree. He ( the Prophet, sal Allaahu alayhi wa sallam ) relieved himself. He came to us after he had cleansed himself with water.