"I divorced my wife when she was menstruating. 'Umar mentioned that to the Messenger of Allah and he said: 'Tell him to take her back until she becomes pure (i.e., her period ends), then she has her period (again), then she becomes pure (again), then if he wishes he may divorce her before having sexual relations with her, and if he wishes he may keep her. This is the waiting period that Allah has enjoined.'"  

طَلَّقْتُ امْرَأَتِي وَهِيَ حَائِضٌ فَذَكَرَ ذَلِكَ عُمَرُ لِرَسُولِ اللَّهِ ﷺ فَقَالَ مُرْهُ فَلْيُرَاجِعْهَا حَتَّى تَطْهُرَ ثُمَّ تَحِيضَ ثُمَّ تَطْهُرَ ثُمَّ إِنْ شَاءَ طَلَّقَهَا قَبْلَ أَنْ يُجَامِعَهَا وَإِنْ شَاءَ أَمْسَكَهَا فَإِنَّهَا الْعِدَّةُ الَّتِي أَمَرَ اللَّهُ  

"Divorce according to the Sunnah means divorcing her when she is pure, ( i.e., not menstruating) and without having had intercourse with her (during that cycle)."  

أَنْ يُطَلِّقَهَا طَاهِرًا مِنْ غَيْرِ جِمَاعٍ  

"Divorce according to the Sunnah means divorcing her with one divorce in each cycle when she is pure, then when she becomes pure the third time, then he pronounces divorce again, and after that she must wait one more menstrual cycle."  

طَلاَقُ السُّنَّةِ يُطَلِّقُهَا عِنْدَ كُلِّ طُهْرٍ تَطْلِيقَةً فَإِذَا طَهُرَتِ الثَّالِثَةَ طَلَّقَهَا وَعَلَيْهَا بَعْدَ ذَلِكَ حَيْضَةٌ  

"I asked Ibn 'Umar about a man who divorced his wife when she was menstruating. He said: 'Do you know 'Abdullah bin 'Umar? He divorced his wife when she was menstruating then 'Umar came to the Prophet ﷺ (and told him what had happened). He ordered him to take her back.' I said: 'Will that be counted (as a divorce)?' He said: 'Do You think he was helpless and behaving foolishly? [i.e., Yes, it counts (as a divorce).]."'  

تَعْرِفُ عَبْدَ اللَّهِ بْنَ عُمَرَ طَلَّقَ امْرَأَتَهُ وَهِيَ حَائِضٌ فَأَتَى عُمَرُ النَّبِيَّ ﷺ فَأَمَرَهُ أَنْ يُرَاجِعَهَا قُلْتُ أَيُعْتَدُّ بِتِلْكَ قَالَ أَرَأَيْتَ إِنْ عَجَزَ وَاسْتَحْمَقَ