It was narrated that Yunus bin Zubair, Abu Ghallab, said: "I asked Ibn Umar about a man who divorced his wife when she was menstruating. He said: Do you know Abdullah bin Umar? He divorced his wife when she was menstruating then Umar came to the Prophet ﷺ (and told him what had happened). He ordered him to take her back. I said: Will that be counted (as a divorce)? He said: Do you think he was helpless and behaving foolishly? [i.e., yes, it counts (as a divorce). (Sahih)