Sunan an-Nasa'i · Book 27 · Hadith 3398
أَخْبَرَنِي زِيَادُ بْنُ أَيُّوبَ، قَالَ حَدَّثَنَا هُشَيْمٌ، قَالَ أَخْبَرَنَا أَبُو بِشْرٍ، عَنْ سَعِيدِ بْنِ جُبَيْرٍ، عَنِ ابْنِ عُمَرَ، أَنَّهُ طَلَّقَ امْرَأَتَهُ وَهِيَ حَائِضٌ فَرَدَّهَا عَلَيْهِ رَسُولُ اللَّهِ صلى الله عليه وسلم حَتَّى طَلَّقَهَا وَهِيَ طَاهِرٌ .
It was narrated from Ibn 'Umar that he divorced his wife when she was menstruating, but the Messenger of Allah (ﷺ) told him to take her back, and divorce her when she was pure (not menstruating).
sahih