(1) The Book of Purification
كتاب الطهارة
(143) Chapter: Mention Of Concealing Oneself When Performing Ghusl
(143) باب ذِكْرِ الاِسْتِتَارِ عِنْدَ الاِغْتِسَالِ
Sunan an-Nasa'i 225 
It was narrated from Umm Hani' that she went to the Prophet (ﷺ) on the day of the Conquest (of Makkah) and found him performing Ghusl while Fatimah was concealing him with a garment. She gave him Salams and he said:
"Who is this?" She said: "Umm Hani'." When he had finished his Ghusl he stood up and prayed eight Rak'ahs wrapped in a garment.
أَخْبَرَنَا يَعْقُوبُ بْنُ إِبْرَاهِيمَ، عَنْ عَبْدِ الرَّحْمَنِ، عَنْ مَالِكٍ، عَنْ سَالِمٍ، عَنْ أَبِي مُرَّةَ، مَوْلَى عَقِيلِ بْنِ أَبِي طَالِبٍ عَنْ أُمِّ هَانِئٍ، رضى الله عنها أَنَّهَا ذَهَبَتْ إِلَى النَّبِيِّ صلى الله عليه وسلم يَوْمَ الْفَتْحِ فَوَجَدَتْهُ يَغْتَسِلُ وَفَاطِمَةُ تَسْتُرُهُ بِثَوْبٍ فَسَلَّمَتْ فَقَالَ ‏ "‏ مَنْ هَذَا ‏"‏ ‏.‏ قُلْتُ أُمُّ هَانِئٍ ‏.‏ فَلَمَّا فَرَغَ مِنْ غُسْلِهِ قَامَ فَصَلَّى ثَمَانِيَ رَكَعَاتٍ فِي ثَوْبٍ مُلْتَحِفًا بِهِ ‏.‏
Grade :  Sahih (Darussalam)
Reference : Sunan an-Nasa'i 225
In-book reference : Book 1, Hadith 226
English translation : Vol. 1, Book 1, Hadith 226