Musannaf Ibn Abi Shayba 1:1309

Abu Bakr narrated to us, he said: Waki' narrated to us, he said: Al-A'mash narrated to us, from Abu Wa'il, from Hudhayfah, that the Messenger of Allah (may Allah bless him and grant him peace) came to a trash heap of some people and urinated upon it while standing.