Marrying a woman in the state of iddat

Marrying a woman who is in the state of iddat is haraam in Islam. If the one who married her knew that she had not yet completed her iddat, then he should immediately separate her (whether he had relations with her or not) and allow her to complete her iddat. The iddat will be calculated from the time she was divorced. Recommencing a new iddat will not be compulsory upon her. After the completion of her iddat, if he wishes to marry her, he may marry her.

If he did not know at the time of the nikaah that she was in iddat and after marrying her he had relations with her, then he should immediately separate her and she should sit for a complete iddat from the time he separates her (i.e. she will recommence her iddat from the time he separates her). Thereafter if he wishes to marry her, he may do so. However if he did not have relations with her, then he should immediately separate her and allow her to complete her iddat. After completing the iddat, if he wishes he may marry her.

And Allah Ta'ala (الله تعالى) knows best.