Is the expiation for an oath obligatory, and what is required of one who swore to quit smoking but cannot do so?

Question:
Honorable Shaykh, may Allah grant you success, he says: What is the amount of the expiation for an oath? And is it permissible to break an oath after swearing it, such as if one swears, for example, to quit smoking and not return to it, and then returns to it due to weakness of the soul?

Answer:
Yes, the expiation is obligatory if you swore to leave something and then did it intentionally. The expiation is of two types: a choice and a sequence. In the case of a choice, it is between three things: feeding ten poor people, clothing them, or freeing a slave; you have the choice. If you do not find any of these three, you fast for three days. This is the expiation for an oath. If one swears not to leave smoking, it is obligatory for him from two aspects: from the aspect of leaving the forbidden, and from the aspect of being faithful to the oath. So it is not permissible for him to violate the oath. If he violates it and disobeys, he is sinful, and the expiation is also obligatory upon him, along with repentance to Allah the Exalted. Yes.