Sunan an-Nasa'i 36
سنن النسائي#36Da'ifأَخْبَرَنَا عَلِيُّ بْنُ حُجْرٍ، قَالَ أَنْبَأَنَا ابْنُ الْمُبَارَكِ، عَنْ مَعْمَرٍ، عَنِ الأَشْعَثِ بْنِ عَبْدِ اللَّهِ، عَنِ الْحَسَنِ، عَنْ عَبْدِ اللَّهِ بْنِ مُغَفَّلٍ، عَنِ النَّبِيِّ صلى الله عليه وسلم قَالَ " لاَ يَبُولَنَّ أَحَدُكُمْ فِي مُسْتَحَمِّهِ فَإِنَّ عَامَّةَ الْوَسْوَاسِ مِنْهُ " .
It was narrated from 'Abdullah bin Mughaffal that the Prophet (ﷺ) said:"None of you should urinate in the place where he bathes, for most Waswas (devilish whispers) [1] come from that." [1] I.e., with regard to whether the urine has soiled his body or not
Scholarly Authentication
The label above is the grade most of these scholars gave — one dissenting opinion no longer speaks for all of them. If any scholar calls a narration fabricated, that verdict is shown instead, whatever the others say. Each scholar's own wording:
In-book reference: 1:36