What is the ruling on one who swore by divorce upon himself not to return to a sin, then returned to it? Is his wife considered forbidden to him, and what must he do to atone for this divorce?

The majority of scholars hold that swearing by divorce—whether the intent is to effect divorce, or to threaten, or to prevent, or to encourage, or to emphasize—results in divorce upon breaking the oath. This is the authoritative fatwa (definition). This differs from the view of Ibn Taymiyyah, who believes that it does not result in divorce but rather incurs the expiation for an oath. The preponderant opinion is that of the majority. Therefore, if you do what you swore to abandon, divorce has occurred. If it has not completed three divorces, you may reconcile with your wife before the expiration of her 'iddah (definition) (waiting period). We advise against swearing by divorce, as it is among the oaths of the dissolute, and using oaths to compel oneself to abandon sins is not a sound approach.