Nafi’ (may Allah have mercy on him) says that once Abdullah ibn Umar (may Allah be pleased with them both) gave his wife a divorce while she was in her menstrual period. Umar (may Allah be pleased with him) asked the Prophet (peace and blessings be upon him) about this issue, so the Prophet (peace and blessings be upon him) ordered that he should take her back and wait until she has her menstrual period again and then wait until she becomes pure. Then, before approaching his wife, if he wishes, he may divorce her, and if he wishes, he may keep her. This is the method according to which Allah has given men permission to divorce their wives.