Is expiation obligatory upon the spouses if the husband has intercourse with his wife, thinking that she is suffering from irregular bleeding (istihāḍah), then it becomes clear that it was the beginning of her menstruation?

If the lochial bleeding (nifas) extends beyond its maximum duration, the excess blood is considered irregular bleeding (dam fasad) and does not prohibit intercourse. Consequently, no expiation is due for intercourse that occurs during the time of this excess blood, because expiation is only required when it is certain that intercourse took place during a confirmed menstruation (hayd) or lochia (nifas).