Sunan An-Nasa'i - سنن النسائي
27. The Book of Divorce - كتاب الطلاق
4) Chapter: Divorce Without The 'Iddah
It was narrated from Ibn 'Umar that he divorced his wife when she was menstruating, but the Messenger of Allah told him to take her back, and divorce her when she was pure (not menstruating).
4) باب الطَّلاَقِ لِغَيْرِ الْعِدَّةِ
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 .