What is the ruling on someone who swore multiple times that he would fast a certain number of days if he committed a sin, then became unable to fulfill this vow? Is he required to offer an expiation for breaking an oath for each sworn statement, or a single expiation?

The preponderant opinion is that repeated oaths concerning a single matter necessitate only one expiation, unless the wording of the oath implies repetition, such as saying: "Every time," or if the one swearing the oath intended the expiation to be repeated with the repetition of the act sworn against. The same applies to vows of lajaj and anger, which are akin to oaths for urging or preventing, without intending a true vow. The questioner's statement: "for every instance of committing that sin" indicates his intention to repeat the fasting after each time he commits the sin. Therefore, a separate expiation for an oath is required for each breach. The questioner should be mindful that expiations alone do not absolve him of his sin until he repents to Allah Almighty from it.