Intercourse with a menstruating woman after her purity but before the ritual bath, and its expiation

Question:
He says: Honorable Shaykh, may Allah grant you success. A woman became pure from her menstruation, and before she performed the ritual bath, her husband had intercourse with her. Do they owe an expiation? And what is its amount if they do?

Answer:
Yes, they owe an expiation; because Allah permitted intercourse with a menstruating woman after she becomes pure and performs the ritual bath. There are two conditions: first, that they become pure by the cessation of the blood, and second, that they purify themselves by the ritual bath. What is contingent upon two things is not achieved by either one alone, so the expiation is upon them, which is half a mithqal of gold or its equivalent in other currencies. Yes, either a full mithqal, which is better, or half a mithqal, or its equivalent in other currencies, or they should ask the money changers about that. Yes.