Musnad Ahmad 27:1601

Yunus narrated to us, Layth narrated to us, from Nafi’, that Abdullah divorced his wife while she was menstruating, with a single pronouncement, during the time of the Messenger of Allah (ﷺ). Umar said: "O Messenger of Allah, Abdullah has divorced his wife with a single pronouncement while she was menstruating." The Messenger of Allah (ﷺ) commanded him to take her back and keep her until she became pure, then she should menstruate another time in his presence, then he should wait until she became pure from that menstruation. Then, if he wished to divorce her, he should divorce her when she is pure, before he has intercourse with her; for that is the waiting period which Allah, the Exalted, commanded that women be divorced for. When Abdullah was asked about that, he would say to one of them: "As for you, if you have divorced your wife once or twice, then the Messenger of Allah (ﷺ) commanded me regarding that. But if you have divorced her three times, then she has become forbidden to you until she marries a husband other than you, and you have disobeyed Allah, the Exalted, in what He commanded you regarding the divorce of your wife."