Is it obligatory to make up for days of vowed fasting that I broke due to a legitimate Shar'i excuse, or is there an expiation that can be offered instead of fasting?

If a woman vows to fast two specific days of the week, and she menstruates for more than five days, such that no two days remain for her to fast, then scholars have differed regarding the obligation of making up the fasts (qada'):

- Hanbalis and Hanafis: She is obliged to make up the fasts.

- Malikis and Shafi'is: She is not obliged to make up the fasts, because menstruation prevents fasting just as Eid prevents it.

However, if she vowed to fast two days a week without specifying them, and her menstruation was five days or less, and she was able to fast but did not, then she is obliged to make up the fasts.