What is the ruling on fasting Mondays and Thursdays and the White Days with the intention of making up years of missed fasts whose number is unknown? And is expiation required for making up an entire Ramadan after twelve years? And is it permissible to intend to fast the White Days and perform ghusl on their first day after menstruation?

One must make up for missed days of Ramadan (definition) if one is able to fast. If the exact number of days is unknown, one should err on the side of caution until one is certain of having fulfilled the obligation. Voluntary fasts, such as Mondays and Thursdays or the White Days (Ayyam al-Bid), are not sufficient to make up for missed obligatory fasts. One must hasten to make up these fasts. Delaying making up the fasts until the next Ramadan without a valid excuse necessitates an expiation of feeding one poor person for each day. Fasting the White Days is not permissible if there is doubt about being pure from menstruation or post-natal bleeding, and it is not valid if performed. Rather, one must be certain of purity before Fajr. Ghusl (definition) (ritual bath) is not required for the validity of the fast after one is certain of purity.