Forgetting the number of days he vowed to fast

Q 6: A person forgot how many days they vowed to fast, whether seven or ten days, what should be done? Can they observe voluntary Sawm (Fast) before fulfilling the vow or should they fulfill the mandatory Sawm before the voluntary one?

A: They should fast the number of days that they think most likely to be correct. It is not obligatory to fast the number of days they doubt. It is not permissible to undertake voluntary Sawm before fulfilling the Sawm they vowed to perform, because fulfilling the vow is obligatory.May Allah grant us success. May peace and blessings be upon our Prophet Muhammad, his family, and Companions.