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. The Prophet (peace and blessings be upon him) said: Tell Abdullah to take her back and wait until she becomes pure, then wait until she has her next menstrual period and becomes pure again. Then, before approaching her, he may divorce her or keep her with him. This is the method by which Allah has permitted men to divorce their wives.