“Tell him to take her back, then leave her until she becomes pure, then menstruates, then becomes pure again. Thereafter, if he wishes, he may keep her; and if he wishes, he may divorce her. That is the waiting period at which Allah has commanded that women be divorced.” (1)
The basis for its prohibition is that the Messenger, peace and blessings be upon him, became angry and instructed Umar, may Allah be pleased with him, to tell his son to take her back.
Therefore, if someone wishes to divorce, we must ask him: “Is your wife pregnant?” If he says, “Yes,” we say: “Divorce her; there is no blame.” If he says that she is not pregnant, we ask him: “Is she menstruating or in a state of purity?” If he says, “She is menstruating,” we say: “Do not divorce her. Wait until she becomes pure, and do not have intercourse with her; then divorce her.” If he says, “She is in a state of purity,” we ask whether he has had intercourse with her or not. If he says that he has had intercourse with her, we say: “Do not divorce her. Wait until her pregnancy becomes apparent, or until she menstruates; after that menstruation, divorce her.” If he says that he has not had intercourse with her, we say: “There is no objection to divorcing her.” Thus, the matter must be dealt with in detail.
If someone were to ask: “Why do we inquire? Why not understand the matter in its correct, permissible sense?” We reply: Because people are ignorant of the rulings, and this is why detailed inquiry is necessary. For example, if someone says to you: “A man died, leaving behind a daughter, a brother, and a full paternal uncle,” then you must inquire about the brother. If he says, “He is a maternal half-brother,” then what remains after the daughter’s prescribed share goes to the paternal uncle. But if he says that he is a full brother or a paternal half-brother, then what remains after the daughter’s prescribed share goes to the brother. Thus, any matter involving a strong possibility of ambiguity should be clarified by inquiry, so that one is not left in difficulty.