Sunan an-Nasa'i 264
سنن النسائي#264Sahihأَخْبَرَنَا مُحَمَّدُ بْنُ عُبَيْدٍ، قَالَ حَدَّثَنَا عَبْدُ اللَّهِ بْنُ الْمُبَارَكِ، قَالَ أَنْبَأَنَا مَعْمَرٌ، عَنْ قَتَادَةَ، عَنْ أَنَسٍ، أَنَّ رَسُولَ اللَّهِ صلى الله عليه وسلم كَانَ يَطُوفُ عَلَى نِسَائِهِ فِي غُسْلٍ وَاحِدٍ .
It was narrated from Anas that the Messenger of Allah (ﷺ) used to (go around) all his wives and perform Ghusl once
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 ZaiSahih
In-book reference: 1:265