What must I do if I vowed to abstain from a sin for a specified period, then committed the sin before the period ended? And is this vow considered a vow of obedience (nadr ibraar), an oath (yameen), a vow of anger (nadr lajaj), or is it not considered valid?

"It is absolutely forbidden to commit a sin. A vow to abandon a sin is not considered valid by most scholars and is not binding. The one who commits it must repent, and there is no expiation required of him. Some scholars, however, hold that such a vow is binding, and thus, committing the sin necessitates an expiation of an oath (kaffarat yamin). This latter view is more cautious."