I heard the Messenger of Allah ﷺ say: One of you who believes in Allah and in the Last Day should not raise her head until the men raise their heads (after prostration) lest they should see the private parts of men.  

سَمِعْتُ رَسُولَ اللَّهِ ﷺ يَقُولُ مَنْ كَانَ مِنْكُنَّ يُؤْمِنُ بِاللَّهِ وَالْيَوْمِ الآخِرِ فَلاَ تَرْفَعْ رَأْسَهَا حَتَّى يَرْفَعَ الرِّجَالُ رُءُوسَهُمْ كَرَاهَةَ أَنْ يَرَيْنَ مِنْ عَوْرَاتِ الرِّجَالِ