(27) The Book of Divorce
كتاب الطلاق
(76) Chapter: Taking The Wife Back
(76) باب الرَّجْعَةِ ‏‏
Sunan an-Nasa'i 3558 
It was narrated from Ibn 'Umar that he divorced his wife when she was menstruating, and the Messenger of Allah told him to take her back.
أَخْبَرَنَا يُوسُفُ بْنُ عِيسَى، - مَرْوَزِيٌّ - قَالَ حَدَّثَنَا الْفَضْلُ بْنُ مُوسَى، قَالَ حَدَّثَنَا حَنْظَلَةُ، عَنْ سَالِمٍ، عَنِ ابْنِ عُمَرَ، أَنَّهُ طَلَّقَ امْرَأَتَهُ وَهِيَ حَائِضٌ فَأَمَرَهُ رَسُولُ اللَّهِ صلى الله عليه وسلم فَرَاجَعَهَا ‏.‏
Grade :  Sahih (Darussalam)
Reference : Sunan an-Nasa'i 3558
In-book reference : Book 27, Hadith 172
English translation : Vol. 4, Book 27, Hadith 3588