What is the ruling on someone who swears an oath not to commit a specific sin—whether absolutely or for a limited period—but then is overcome by their lower self and commits it? Is it permissible to specify a duration for abstaining from a sin by oath? And is this oath considered a "laghw" (idle) oath?

The perpetrator of a sin must repent sincerely by abandoning it, regretting it, and resolving not to return to it, while increasing remembrance of Allah (dhikr) and recitation of the Quran, avoiding places of disobedience, and associating with righteous people. As for swearing an oath to abandon a sin, it is an affirmation of the religious obligation to abandon it, and expiation is required if the oath is broken.