Vowing to fast for ten days and then changing it to a month

Q 2: I vowed to fast for ten days and then decided to fast for one month. Which period should I fast?

A: Vowing to fast particular days becomes obligatory by taking upon oneself to make it. Therefore, you must fast for the days you vowed, which are ten days only.May Allah grant us success. May peace and blessings be upon our Prophet Muhammad, his family, and Companions.