Salim narrates from Sayyiduna Abdullah bin Umar (may Allah be pleased with him) that he divorced his wife while she was menstruating. Sayyiduna Umar (may Allah be pleased with him) mentioned it before the Prophet (peace and blessings be upon him), and he (peace and blessings be upon him) said: "Command him to take her back, then let him divorce her while she is in a state of purity or pregnant."
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الخلع والطلاق / 14913