Musnad Ahmad 1034:105

Abu Nu'aym narrated to us, Yunus—meaning Ibn Abi Ishaq—narrated to us, from Abu Ishaq, from Nahik ibn Abdullah al-Saluli: Hudhayfah narrated, saying: "I saw the Messenger of Allah, peace and blessings of Allah be upon him, come to a trash heap of some people, and he urinated while standing."