It was narrated from Ibn 'Umar that he divorced his wife when she was menstruating, but the Messenger of Allah told him to take her back, and divorce her when she was pure (not menstruating).
Sunan an-Nasa'i Book 27, Hadith 10
← Previous Hadith "Tell him to take her back, then divorce her while she is pure (not menstruating) or pregnant."

Sunan an-Nasa'i Book 27, Hadith 9 Next Hadith → "I asked Ibn 'Umar about a man who divorced his wife while she was menstruating. He said: 'Do you know 'Abdullah bin 'Umar?' He divorced his wife while she was menstruating, and 'Umar asked the Prophet about that, and he told him to take her back, then wait for the right time. I said to him: 'Was that divorce counted?' He said: 'Be quiet! What do you think if some becomes helpless and behaves foolishly?'"

Sunan an-Nasa'i Book 27, Hadith 11