Sunan an Nasai 224
The Book of Purification
أَخْبَرَنَا مُجَاهِدُ بْنُ مُوسَى، قَالَ حَدَّثَنَا عَبْدُ الرَّحْمَنِ بْنُ مَهْدِيٍّ، قَالَ حَدَّثَنِي يَحْيَى بْنُ الْوَلِيدِ، قَالَ حَدَّثَنِي مُحِلُّ بْنُ خَلِيفَةَ، قَالَ حَدَّثَنِي أَبُو السَّمْحِ، قَالَ كُنْتُ أَخْدُمُ رَسُولَ اللَّهِ صلى الله عليه وسلم فَكَانَ إِذَا أَرَادَ أَنْ يَغْتَسِلَ قَالَ " وَلِّنِي قَفَاكَ " . فَأُوَلِّيهِ قَفَاىَ فَأَسْتُرُهُ بِهِ .
Abu As-Samh said:"I used to serve the Messenger of Allah (ﷺ) and when he wanted to perform Ghusl he said: 'Turn your back.' So I turned my back to him and concealed him
Grading: Abu Ghuddah: Sahih · Al-Albani: Sahih · Zubair Ali Zai: Isnaad Sahih
Text from the public-domain hadith-api dataset. Numbering follows that dataset and can differ by a few from some printed editions — check the wording, not only the number.