The Messenger of Allah ﷺ said: A man should not see the private parts of another man, and a woman should not see the private parts of another woman, and a man should not lie with another man under one covering, and a woman should not lie with another woman under one covering. (Using translation from Muslim 338a)
أَنَّ النَّبِيَّ ﷺ قَالَ لَا يَنْظُرِ الرَّجُلُ إِلَى عَوْرَةِ الرَّجُلِ وَلَا تَنْظُرِ الْمَرْأَةُ إِلَى عَوْرَةِ الْمَرْأَةِ وَلَا يُفْضِ الرَّجُلُ إِلَى الرَّجُلِ فِي الثَّوْبِ وَلَا تُفْضِ الْمَرْأَةُ إِلَى الْمَرْأَةِ فِي الثَّوْبِ