Sunan an-Nasa'i 401
سنن النسائي#401Sahihأَخْبَرَنَا إِسْحَاقُ بْنُ إِبْرَاهِيمَ، قَالَ حَدَّثَنَا مُعَاذُ بْنُ هِشَامٍ، قَالَ حَدَّثَنِي أَبِي، عَنْ عَطَاءٍ، عَنْ أَبِي الزُّبَيْرِ، عَنْ جَابِرٍ، عَنِ النَّبِيِّ صلى الله عليه وسلم قَالَ " مَنْ كَانَ يُؤْمِنُ بِاللَّهِ وَالْيَوْمِ الآخِرِ فَلاَ يَدْخُلِ الْحَمَّامَ إِلاَّ بِمِئْزَرٍ " .
It was narrated from Jabir that the Prophet (ﷺ) said:"Whoever believes in Allah and the Last Day, let him not enter a bath house except wearing an Izar (waist wrap)
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:
Abu GhuddahSahih
Al-AlbaniSahih
Zubair Ali ZaiHasan
In-book reference: 4:6