Abu Dawud Book 1, Hadith Number 43.

Chapter : Cleansing with water after releiving oneself.

Narated By Anas b. Malik : The Apostle of Allah (PBUH) 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) relieved himself. He came to us after he had cleansed himself with water.