Nafi reported,

Ibn Umar bin Khattab divorced his wife with a single pronouncement of divorce while she was menstruating. The Messenger of Allah ﷺ ordered him to take her back, then keep her until she became pure, then menstruated again in his presence, then became pure once more. If he then wished to divorce her, he could do so when she had become pure, before having intercourse with her. That is the waiting period within which Allah commanded that women be divorced.Whenever Abdullah was asked about this, he would say to the questioner, "If you have divorced her three times, she has become unlawful for you until she marries another husband."Another narrator added in his transmission from Layth, "Nafi told me that Ibn Umar said, 'Had you divorced her once or twice, it would have been valid, for the Prophet ﷺ commanded me to do so.'"

حدثنا قتيبة حدثنا الليث

عن نافع

أن ابن عمر بن الخطاب رضي الله عنهما طلق امرأة له وهي حائض تطليقة واحدة فأمره رسول الله ﷺ أن يراجعها ثم يمسكها حتى تطهر ثم تحيض عنده حيضة أخرى ثم يمهلها حتى تطهر من حيضها فإن أراد أن يطلقها فليطلقها حين تطهر من قبل أن يجامعها فتلك العدة التي أمر الله أن تطلق لها النساء وكان عبد الله إذا سئل عن ذلك قال لأحدهم إن كنت طلقتها ثلاثا فقد حرمت عليك حتى تنكح زوجا غيرك وزاد فيه غيره عن الليث حدثني نافع قال ابن عمر لو طلقت مرة أو مرتين فإن النبي ﷺ أمرني بهذا