Musnad Ahmad 562:0

Narrated to us by Hisham, who said: Narrated to us Qatadah, from Shahr ibn Hawshab, from Abd al-Rahman ibn Ghanam, from al-Hakam ibn Amr al-Ghifari, who said: The Messenger of Allah (ﷺ) forbade that a man should urinate in a place where he bathes, for indeed, most whispers (waswas) come from it.