Is it permissible to observe a vowed fast – which was vowed to be fasted from Saturday to Wednesday – earlier than its appointed time, due to its appointed time coinciding with the menstrual period?

If a woman vows to fast specific days and her menstruation coincides with them, she must make up the vow after she becomes pure. Some jurists are of the opinion that expiation (kaffarah) is not obligatory, but expiation is more cautious and preferable. If menstruation interrupts the vowed days of fasting, she should break her fast and make up for what she missed. She is obligated to make up the vow after her purity, and it is more cautious for her to offer an expiation (kaffarat yamin) for missing the specified time. The vow itself is originally disliked, yet it is obligatory to fulfill it if it is a vow of obedience.