The Prophet ﷺ said: A man should not look at the private parts of another man, and a woman should not look at the private parts of another woman. A man should not lie with another man without wearing lower garment under one cover; and a woman should not be lie with another woman without wearing lower garment under one cover. (Using translation from Abū Dāʾūd 4018)
أَنَّ رَسُولَ اللهِ ﷺ قَالَ لَا يَنْظُرُ الرَّجُلُ إِلَى عَوْرَةِ الرَّجُلِ وَلَا تَنْظُرُ الْمَرْأَةُ إِلَى عَوْرَةِ الْمَرْأَةِ وَلَا يُفْضِي الرَّجُلُ إِلَى الرَّجُلِ فِي الثَّوْبِ وَلَا تُفْضِي الْمَرْأَةُ إِلَى الْمَرْأَةِ فِي الثَّوْبِ