Musnad Ahmad 1034:173

Yahya ibn Sa'id narrated to us, from al-A'mash, Shaqiq narrated to me, from Hudhayfah, who said: "I was with the Prophet, peace and blessings of Allah be upon him, on a path, and he stepped aside. He came to a trash heap of some people and I moved away, but he beckoned me until I was close to his heels. He urinated while standing, then he called for water and performed ablution, and he wiped over his leather socks."