‘Abd Allah bin Umar said that he divorced his wife while she was menstruating during the time of the Messenger of Allah(ﷺ). So ‘Umar bin Al Khattab asked the Messenger of Allah(ﷺ) about this matter. The Messenger of Allah(ﷺ) said “Order him, he must take her back and keep her back till she is purified, then has another menstrual period and is purified. Thereafter if he desires he may divorce her before having intercourse with her, for that is the period of waiting which Allaah the Glorified has commanded for the divorce of women.”
Source: sunnah.com
Other translations
Arabic
حَدَّثَنَا الْقَعْنَبِيُّ، عَنْ مَالِكٍ، عَنْ نَافِعٍ، عَنْ عَبْدِ اللَّهِ بْنِ عُمَرَ، أَنَّهُ طَلَّقَ امْرَأَتَهُ وَهِيَ حَائِضٌ عَلَى عَهْدِ رَسُولِ اللَّهِ صلى الله عليه وسلم فَسَأَلَ عُمَرُ بْنُ الْخَطَّابِ رَسُولَ اللَّهِ صلى الله عليه وسلم عَنْ ذَلِكَ فَقَالَ رَسُولُ اللَّهِ صلى الله عليه وسلم " مُرْهُ فَلْيُرَاجِعْهَا ثُمَّ لْيُمْسِكْهَا حَتَّى تَطْهُرَ ثُمَّ تَحِيضَ ثُمَّ تَطْهُرَ ثُمَّ إِنْ شَاءَ أَمْسَكَ بَعْدَ ذَلِكَ وَإِنْ شَاءَ طَلَّقَ قَبْلَ أَنْ يَمَسَّ فَتِلْكَ الْعِدَّةُ الَّتِي أَمَرَ اللَّهُ سُبْحَانَهُ أَنْ تُطَلَّقَ لَهَا النِّسَاءُ " .
sunnah.com