Sahih Muslim Book 009, Hadith Number 3478.
Chapter: It is forbidden to divorce the woman during her menses.
Abdullah b. 'Umar (Allah be pleased with them) reported: I divorced my wife while she was in the state of menses. 'Umar (Allah be pleased with him) made mention of it to Allah's Apostle (may peace be upon him) and he was enraged and he said: Command him to take her back until she enters the second ensuing menses other than the one in which he divorced her and in case he deems proper to divorce her, he should pronounce divorce (finally) before touching her (in the period) when she is purified of her menses, and that is the prescribed period in regard to divorce as Allah has commanded. 'Abdullah made a pronouncement of one divorce and it was counted in case of divorce. 'Abdullah took her back as Allah's Messenger (may peace be upon him) had commanded him. A hadith like this was reported on the authority of Zuhri with the same chain of narrators. Ibn Umar (Allah be pleased with them), however, said: I took her back, and counted this pronouncement of divorce (as valid) with which I divorced her.