Does the waiting period (iddah) for a divorced woman end with the occurrence of three menstrual cycles in one month, and what is the ruling on sexual intercourse that took place in this situation?

Scholars differ on the minimum period for the completion of three quru’ (menstrual cycles). The more authoritative view is that a woman’s claim of completing her quru’ within one month is not to be accepted without proof, as this is highly improbable. When spouses dispute, they must refer the matter to the Sharia courts for resolution. As for the ruling on the intercourse that occurred, it depends on the adopted view regarding the issue:

If it is held that the three quru’ cannot be completed within one month, then the intercourse is permissible and sufficient for raj‘ah (revocation of divorce). If it is held that she has exited the iddah (waiting period): If the husband was aware of this, then the intercourse is zina (fornication/adultery). If he was not aware, it is wat’ shubhah (intercourse based on misconception), for which there is no sin, and legal rulings apply (such as the child being attributed to him and inheritance), but raj‘ah is not established through it.