That ʿAbdullah bin ʿUmar told him that he had divorced his wife while she was in her menses so ʿUmar informed Messenger of Allah ﷺ of that. Messenger of Allah ﷺ became very angry at that and said, "(Ibn ʿUmar must return her to his house and keep her as his wife till she becomes clean and then menstruates and becomes clean again, whereupon, if he wishes to divorce her, he may do so while she is still clean and before having any sexual relations with her, for that is the legally prescribed period for divorce as Allah has ordered."
أَخْبَرَهُ أَنَّهُ طَلَّقَ امْرَأَتَهُ وَهْىَ حَائِضٌ فَذَكَرَ عُمَرُ لِرَسُولِ اللَّهِ ﷺ فَتَغَيَّظَ فِيهِ رَسُولُ اللَّهِ ﷺ ثُمَّ قَالَ لِيُرَاجِعْهَا ثُمَّ يُمْسِكْهَا حَتَّى تَطْهُرَ ثُمَّ تَحِيضَ فَتَطْهُرَ فَإِنْ بَدَا لَهُ أَنْ يُطَلِّقَهَا فَلْيُطَلِّقْهَا طَاهِرًا قَبْلَ أَنْ يَمَسَّهَا فَتِلْكَ الْعِدَّةُ كَمَا أَمَرَهُ اللَّهُ