What is the expiation for someone who swore to abandon a forbidden act, and conditioned upon committing it the fasting of three days for each instance, then repeated the act until the total number of days reached twenty, and he is unable to fast them due to studying and physical exertion, and is this considered a vow?

The Laghaj Oath (oath of insistence), by which the swearer intends to prevent something or encourage it, gives the person who swore it the choice between fulfilling what he swore to or offering expiation (kaffarah yamin). If you do what you swore to abandon, you must fast three days or offer expiation for each action. Abandoning what is unlawful (haram) is a religious obligation, and it is emphasized by swearing an oath upon it. Breaking this type of oath leads to sin from two aspects: committing the unlawful act and breaking the oath. Therefore, one must hasten to sincere repentance and increase in righteous deeds.