Sayyiduna Ibn Umar (may Allah be pleased with them both) says that once I divorced my wife with one divorce while she was in her menstrual period. Sayyiduna 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 remain away from her until she becomes pure. Then, before approaching his wife, he may either divorce her or keep her. This is the method according to which Allah has given men permission to divorce their wives.