Sahih Muslim 2181
'A'isha reported that a eunuch used to come to the wives of Allah's Apostle (ﷺ) and they did not And anything objectionable in his visit considering him to be a male without any sexual desire. Allah's Apostle (ﷺ) one day came as he was sitting with some of his wives and he was busy in describing the bodily characteristics of a lady and saying:
As the comes in front tour folds appear on her front side and as she turns her back eight folds appear on the back side. Thereupon Allah's Apostle (ﷺ) said: I me that he knows these things; do not, therefore. allow him to cater. She (" A'isha) said: Then they began to observe veil from him.
وَحَدَّثَنَا عَبْدُ بْنُ حُمَيْدٍ، أَخْبَرَنَا عَبْدُ الرَّزَّاقِ، عَنْ مَعْمَرٍ، عَنِ الزُّهْرِيِّ، عَنْ عُرْوَةَ،
 عَنْ عَائِشَةَ، قَالَتْ كَانَ يَدْخُلُ عَلَى أَزْوَاجِ النَّبِيِّ صلى الله عليه وسلم مُخَنَّثٌ فَكَانُوا يَعُدُّونَهُ
 مِنْ غَيْرِ أُولِي الإِرْبَةِ - قَالَ - فَدَخَلَ النَّبِيُّ صلى الله عليه وسلم يَوْمًا وَهُوَ عِنْدَ بَعْضِ
 نِسَائِهِ وَهُوَ يَنْعَتُ امْرَأَةً قَالَ إِذَا أَقْبَلَتْ أَقْبَلَتْ بِأَرْبَعٍ وَإِذَا أَدْبَرَتْ أَدْبَرَتْ بِثَمَانٍ ‏.‏ فَقَالَ
 النَّبِيُّ صلى الله عليه وسلم ‏
"‏ أَلاَ أَرَى هَذَا يَعْرِفُ مَا هَا هُنَا لاَ يَدْخُلَنَّ عَلَيْكُنَّ ‏"‏ ‏.‏ قَالَتْ
 فَحَجَبُوهُ ‏.‏