Anas bin Sirin related: I heard Sayyiduna Abdullah bin Umar (may Allah be pleased with him) say: I divorced my wife while she was menstruating, so Sayyiduna Umar (may Allah be pleased with him) informed the Prophet (peace and blessings be upon him). He (peace and blessings be upon him) said: "Let him take her back and divorce her in a state of purity." He said: I said to Sayyiduna Ibn Umar (may Allah be pleased with him): "Will it be counted?" He said: "Hold on."
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الخلع والطلاق / 14921