For twenty years, people I did not suspect of dishonesty kept telling me that Ibn Umar had divorced his wife with three pronouncements while she was menstruating, and that he was ordered to take her back. I neither doubted them nor truly understood the hadith, until I met Abu Ghallab Yunus bin Jubayr al-Bahili. He was a reliable man, and he told me that he had asked Ibn Umar about it, and Ibn Umar told him that he had divorced his wife with a single pronouncement while she was menstruating, and that he was ordered to take her back.Yunus bin Jubayr said, "I asked, 'Was that pronouncement counted against him?'"Ibn Umar replied, "Of course. What else, if he acted incapably and foolishly?"
مكثت عشرين سنة يحدثني من لا أتهم أن ابن عمر طلق امرأته ثلاثا وهي حائض. فأمر أن يراجعها. فجعلت لا أتهمهم ولا أعرف الحديث حتى لقيت أبا غلاب يونس بن جبير الباهلي. وكان ذا ثبت فحدثني أنه سأل ابن عمر، فحدثه أنه طلق امرأته تطليقة وهي حائض، فأمر أن يرجعها. قال: قلت: أفحسبت عليه؟ قال: فمه أو إن عجز واستحمق؟
Bukhari narrated it in the Chapter on Divorce (5333) through Yazid bin Ibrahim, and Muslim narrated it in the Chapter on Divorce (7:1471) through Ayub, both of them from Ibn Sirin, with this wording. The wording given here is Muslim's, while Bukhari's version is abridged and does not mention the beginning of the story. Bukhari also mentioned it as a suspended report (5253) through Ayub, from Saeed bin Jubayr, from Ibn Umar, who said, "It was counted against me as one divorce."From what has preceded, it appears there is no disagreement among the scholars that a man who divorces his wife during her menstruation is obligated to take her back, and then wait until her second period of purity, at which point he may either keep her or divorce her if he wishes.They disagreed, however, about divorcing her during the first period of purity. Abu Hanifa held that this is permissible, on the grounds that the prohibition was due to the menstruation, so once she becomes pure, the cause of the prohibition ceases, making it permissible to divorce her in this period of purity just as it is permissible in the period of purity that follows it. Imam Ahmad has a reported opinion permitting this as well, and there is likewise a view among the Shafiis allowing it, though the sound position in his school is that it is forbidden.They have mentioned many reasons for delaying it until the second period of purity, among them that the taking-back should not be for the purpose of divorce. For if he keeps her for a period of time, he may have intercourse with her, and it is not permissible for him to divorce her during a period of purity in which he had intercourse with her, so he would then be retracting from carrying out the divorce altogether.