Sunan Abī Dāwūd 2179

The full narration

‘Abd Allah bin Umar said that he divorced his wife while she was menstruating during the time of the Apostle of Allaah(ﷺ). So ‘Umar bin Al Khattab asked the Apostle of Allaah(ﷺ) about this matter. The Apostle of Allaah(ﷺ) said “Order him, he must take her back and keep her back till she is purified, then has another menstrual period and is purified. Thereafter if he desires he may divorce her before having intercourse with her, for that is the period of waiting which Allaah the Glorified has commanded for the divorce of women.”