Why did Aisha, may God be pleased with her, say that a divorced woman becomes definitively separated from her husband and lawful for another man as soon as she enters the third menstruation, even though her opinion on the “qur’” is that it is purity, and thus she has not completed the third purity? And is it impermissible for a man to take back his divorced wife during menstruation?

Scholars differ concerning the 'iddah (waiting period) of a divorced woman, whether it is three menstrual cycles or three periods of purity. The more preponderant view is that it is three menstrual cycles. The رجعة (right of return) is valid during the third menstrual cycle until she becomes pure from it. However, according to the view that it is three periods of purity, the period of purity during which the divorce occurred is counted. So, if she menstruates and then becomes pure, that is the second period of purity. And if she menstruates a second time and then becomes pure, that is the third period of purity. If she menstruates after that, the 'iddah concludes upon the onset of the third menstrual cycle. This is the view of 'Aisha, may Allah be pleased with her.