Vowing to fast for 3 days every month

Q 2: A woman made a vow to fast on the White Days (13th, 14th, and 15th of every Hijri month). However, sometimes she menstruates during these days. What should she do?

A: If the case is as mentioned, it is an act of obedience and the Prophet (peace be upon him) stated, (Part No. 23; Page No. 366) Whoever vows to obey Allah, should obey Him and whoever vows to disobey Allah, should not disobey Him. If she menstruates during the White Days, she must discontinue fasting and make up for the three days while in a state of purity. Fasting these days was made obligatory by her vow. Following the example of obligatory fasting during Ramadan, when there is a Shar`y cause preventing her from fasting, she should make up for the missed days. One example of this sort is the fasting required by one who offers Kaffarah (expatiation).May Allah grant us success. May peace and blessings be upon our Prophet Muhammad, his family, and Companions.