‘Abd Allah (bin Umar) said that he divorced his wife while she was menstruating. ‘Umar mentioned the matter to the Messenger of Allah ﷺ. The Messenger of Allah ﷺ became angry and said “Command him, he must take her back and keep her back till she is purified, then has another menstrual period and is purified. Then if he desires he may divorce her during the period of purity before he has intercourse with her. This is the divorce for waiting period as commanded by Allaah, the Exalted. (Using translation from Abū Dāʾūd 2182)
أَخْبَرَهُ أَنَّهُ طَلَّقَ امْرَأَتَهُ وَهِيَ حَائِضٌ فَذَكَرَ ذَلِكَ عُمَرُ لِرَسُولِ اللهِ ﷺ فَتَغَيَّظَ فِيهِ رَسُولُ اللهِ ﷺ ثُمَّ قَالَ رَسُولُ اللهِ ﷺ لِيُرَاجِعْهَا ثُمَّ لِيُمْسِكْهَا حَتَّى تَطْهُرَ ثُمَّ تَحِيضَ ثُمَّ تَطْهُرَ فَإِنْ بَدَا لَهُ أَنْ يُطَلِّقَهَا فَلْيُطَلِّقْهَا طَاهِرًا قَبْلَ أَنْ يَمَسَّهَا فَتِلْكَ الْعِدَّةُ كَمَا أَمَرَ اللهُ ﷻ