سنن النسائي

'Abdullah bin Ayman asked Ibn 'Umar while Abu Az-Zubair was listening: "What did you think about a man who divorces his wife when she is menstruating?" He said to him: "Abdullah bin 'Umar divorced his wife when she was menstruating during the time of the Messenger of Allah. 'Umar asked the Messenger of Allah (about that) and said: 'Abdullah bin 'Umar has divorced his wife while she was menstruating.' The Messenger of Allah (ﷺ) said: 'Let him take her back.' So he made me take her back. He said: 'When she becomes pure, let him divorce her or keep her.' Ibn 'Umar said: 'The Prophet (ﷺ) said: 'O Prophet! When you divorce women, divorce them before their 'Iddah (prescribed period) elapses.'"