Nafi' narrates from Sayyiduna Abdullah bin Umar (may Allah be pleased with him) that he divorced his wife with a single divorce while she was menstruating, so the Messenger of Allah (peace and blessings be upon him) commanded him to take her back, and said: "Let him keep her until she becomes pure. Then, when she has another menstruation, let him give her time until she becomes pure. If he intends to divorce, let him divorce in (her) purity without having intercourse. This is the period in which Allah Almighty has commanded that women be divorced."
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الخلع والطلاق / 14908