Salim bin Abdullah (may Allah have mercy on him) said that Sayyiduna Abdullah bin Umar (may Allah be pleased with him) said: I divorced my wife while she was menstruating, during the lifetime of the Prophet (peace and blessings be upon him). When Sayyiduna Umar (may Allah be pleased with him) mentioned it, he (peace and blessings be upon him) became angry with me and said: "Let him take her back and keep her until purity comes after menstruation. Then, if he wishes, let him divorce her in that purity without having intercourse. This is the divorce for the waiting period which Allah has commanded." Sayyiduna Abdullah (may Allah be pleased with him) said: I took her back and counted it as only one divorce, the one I had pronounced.
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الخلع والطلاق / 14910