His father divorced his wife during her menses, so Umar asked the Prophet about that and he said: "Tell him to take her back, then let him divorce her while she is pure or pregnant." (Using translation from Tirmidhī 1176)
أَنَّهُ طَلَّقَ امْرَأَتَهُ وَهِيَ حَائِضٌ فَسَأَلَ عُمَرُ النَّبِيَّ ﷺ فَقَالَ مُرْهُ فَلْيُرَاجِعْهَا ثُمَّ لِيُطَلِّقْهَا طَاهِرًا أَوْ حَامِلًا