She told that when they intended to wash the Prophet, they said they did not know whether they should strip him of his clothes as they did with their dead, or wash him with his clothes on. When they disagreed, God cast sleep upon them, so that every man's chin was on his breast. Then someone of whose identity they were unaware addressed them from the comer of the house saying, "Wash the Prophet (ﷺ) with his clothes on," so they got up and washed him with his shirt on, pouring the water over the shirt and rubbing him with the shirt. Baihaqi transmitted it in Dala'il an nubuwa.
Source: sunnah.com
Other translations
Arabic
وَعَنْهَا قَالَتْ: لَمَّا أَرَادُوا غُسْلَ النَّبِيِّ صَلَّى اللَّهُ عَلَيْهِ وَسَلَّمَ قَالُوا: لَا نَدْرِي أَنُجَرِّدُ رَسُولُ اللَّهِ صَلَّى اللَّهُ عَلَيْهِ وَسَلَّمَ مَنْ ثِيَابه كَمَا تجرد مَوْتَانَا أَمْ نُغَسِّلُهُ وَعَلَيْهِ ثِيَابُهُ؟ فَلَمَّا اخْتَلَفُوا أَلْقَى اللَّهُ عَلَيْهِمُ النَّوْمَ حَتَّى مَا مِنْهُمْ رجل إِلَّا وذقته فِي صَدْرِهِ ثُمَّ كَلَّمَهُمْ مُكَلِّمٌ مِنْ نَاحِيَةِ الْبَيْتِ لَا يَدْرُونَ مَنْ هُوَ؟ اغْسِلُوا النَّبِيَّ صَلَّى اللَّهُ عَلَيْهِ وَسَلَّمَ وَعَلَيْهِ ثِيَابُهُ فَقَامُوا فَغَسَّلُوهُ وَعَلَيْهِ قَمِيصُهُ يَصُبُّونَ الْمَاءَ فَوْقَ الْقَمِيصِ وَيُدَلِّكُونَهُ بِالْقَمِيصِ. رَوَاهُ الْبَيْهَقِيُّ فِي «دَلَائِلِ النُّبُوَّةِ»
sunnah.com