He divorced his wife while she was menstruating, so Umar asked the Prophet ﷺ about it. He said, "Order him to take her back, then divorce her when she is in a state of purity or pregnant."
حدثنا هناد حدثنا وكيع عن سفيان عن محمد بن عبد الرحمن مولى آل طلحة
أنه طلق امرأته في الحيض فسأل عمر النبي ﷺ فقال مره فليراجعها ثم ليطلقها طاهرا أو حاملا
Agreed upon [by Bukhari and Muslim]. Muslim narrated it, no. 5/1471 (see the previous hadith), from the hadith of Waki, and Bukhari, no. 7160, from the hadith of Salim bin Abdullah bin Umar, through the same chain.