Does a divorce oath apply to a menstruating woman if the husband does not know that she is menstruating?

Divorce during menstruation is a forbidden innovation (bid'ah muharramah), yet it is effective according to the majority of scholars. However, Shaykh al-Islam Ibn Taymiyyah and those who agreed with him held that it is not effective, regardless of whether the husband knew of her menstruation or was ignorant of it. If the husband divorced her while ignorant of her menstruation, he is not sinful. Thus, a divorce that occurs during menstruation is not binding, and the woman remains under her husband's marital bond.