Sunan an-Nasa'i 3556

It was narrated from Ibn 'Umar that he divorced his wife when she was menstruating. 'Umar, may Allah be pleased with him, mentioned that to the Prophet and he said:"Tell him to take her back until she menstruates again, then when she becomes pure, if he wants he may divorce her and if he wants he may keep her. This is the divorce that Allah has enjoined. Allah, the Mighty and Sublime, says: 'The divorce is twice, after that, either you retain her on reasonable terms or release her with kindness