Sahih Bukhari Volume 6, Book 65, Hadith 4910

حَدَّثَنَا يَحْيَى بْنُ بُكَيْرٍ، حَدَّثَنَا اللَّيْثُ، قَالَ حَدَّثَنِي عُقَيْلٌ، عَنِ ابْنِ شِهَابٍ، قَالَ أَخْبَرَنِي سَالِمٌ، أَنَّ عَبْدَ اللَّهِ بْنَ عُمَرَ ـ رضى الله عنهما ـ أَخْبَرَهُ أَنَّهُ، طَلَّقَ امْرَأَتَهُ وَهْىَ حَائِضٌ، فَذَكَرَ عُمَرُ لِرَسُولِ اللَّهِ صلى الله عليه وسلم فَتَغَيَّظَ فِيهِ رَسُولُ اللَّهِ صلى الله عليه وسلم ثُمَّ قَالَ ‏"‏ لِيُرَاجِعْهَا ثُمَّ يُمْسِكْهَا حَتَّى تَطْهُرَ، ثُمَّ تَحِيضَ فَتَطْهُرَ، فَإِنْ بَدَا لَهُ أَنْ يُطَلِّقَهَا فَلْيُطَلِّقْهَا طَاهِرًا قَبْلَ أَنْ يَمَسَّهَا فَتِلْكَ الْعِدَّةُ كَمَا أَمَرَهُ اللَّهُ ‏"‏‏.‏

Narrated By Salim : That Abdullah bin Umar told him that he had divorced his wife while she was in her menses so 'Umar informed Allah's Apostle of that. Allah's Apostle became very angry at that and said, "(Ibn 'Umar must return her to his house and keep her as his wife till she becomes clean and then menstruates and becomes clean again, whereupon, if he wishes to divorce her, he may do so while she is still clean and before having any sexual relations with her, for that is the legally prescribed period for divorce as Allah has ordered."