It is narrated from Ibn Umar (may Allah be pleased with them both) that he divorced his wife during her menstrual period in the time of the Prophet ﷺ. When Umar (may Allah be pleased with him) asked the Messenger of Allah ﷺ about this, the Messenger of Allah ﷺ said: "Tell Ibn Umar to take her back, then keep her with him until she becomes pure from her menstruation, then she has her menses again, and when she becomes pure after that, if he wishes, he may keep her in his marriage, and if he wishes, he may divorce her before having intercourse with her in that period of purity. This is the waiting period in which Allah has commanded women to be divorced."
Hadith Referenceمسند الإمام الشافعي / كتاب الطلاق / 1244