Divorce during the menses is counted as one legal divorce.
حَدَّثَنَا سُلَيْمَانُ بْنُ حَرْبٍ، حَدَّثَنَا شُعْبَةُ، عَنْ أَنَسِ بْنِ سِيرِينَ، قَالَ سَمِعْتُ ابْنَ عُمَرَ، قَالَ طَلَّقَ ابْنُ عُمَرَ امْرَأَتَهُ وَهْىَ حَائِضٌ، فَذَكَرَ عُمَرُ لِلنَّبِيِّ صلى الله عليه وسلم فَقَالَ " لِيُرَاجِعْهَا ". قُلْتُ تُحْتَسَبُ قَالَ " فَمَهْ ". وَعَنْ قَتَادَةَ عَنْ يُونُسَ بْنِ جُبَيْرٍ عَنِ ابْنِ عُمَرَ قَالَ " مُرْهُ فَلْيُرَاجِعْهَا ". قُلْتُ تُحْتَسَبُ قَالَ أَرَأَيْتَ إِنْ عَجَزَ وَاسْتَحْمَقَ.
Narrated Anas bin Seereen: Ibn `Umar said: "I divorced my wife while she was menstruating. `Umar mentioned that to the Prophet . The Prophet (ﷺ) said, (to my father), "Let your son take her back." I asked (Ibn `Umar), "Is such a divorce counted (i.e. as one legal divorce)?" Ibn `Umar said, "Of course." Narrated Yunus bin Jubair: Ibn `Umar said, "The Prophet (ﷺ) said to `Umar, 'Order him (Ibn `Umar) to take her back.' " I asked, "Is such a divorce counted (as one legal divorce)?" Ibn `Umar said, "What do you think if someone becomes helpless and foolish?"