Ruling on fasting a month for one who committed a sin

A listener from Riyadh, Ahmad Abdullah Sulayman, sent a question saying: I committed a sin, and afterwards I made a vow to fast a month if I were to repeat it. Since I committed this sin again, am I obligated to fulfill this vow, or is it considered an oath for which I must pay the expiation for a broken oath?
Answer: If you vowed the month to refrain from it so that it would prevent you from returning to it, then the ruling is the ruling of the expiation for a broken oath. You must pay the expiation for a broken oath, and feeding ten poor people or clothing them is sufficient, if the intention of the vow was to refrain from returning to it. You made this vow hoping that Allah would prevent you from it through it. This is its ruling: the ruling of an oath, and you must pay the expiation for a broken oath. Yes.
The presenter: May Allah reward you with good and do you good.