Musnad Ahmad 834:24

'Attab ibn Ziyad narrated to us, Abdullah narrated to us, Ma'mar informed us, Ash'ath ibn Abdullah narrated to me, from al-Hasan, from Abdullah ibn Mughaffal, who said: "The Messenger of Allah (peace and blessings of Allah be upon him) forbade that a man should urinate in his bathing place, for the majority of the whisperings (waswas) come from it."