What is required of one who vows not to commit a sin but then commits it?

Question:
Benefits from the explanation of the book *Iqtida' al-Sirat al-Mustaqim li-Mukhalafat Ahl al-Jahim* by Ibn Taymiyyah. Before we part with the topic of vows, Shaykh (may Allah preserve you), sometimes some smokers, when they want to bind themselves to quitting smoking, make a vow to quit. Some of them keep their vow, and some are unable to, which requires an expiation. What is your guidance on this?

Answer:
Yes, some people want to leave a thing; they want to leave a thing, especially if that thing is forbidden and a sin. They want to repent from it, then they vow that if they return to it, they will do such and such acts of obedience, or spend such and such amount of money, or fast such and such number of days. They may even vow to fast for a year or for months in order to make the prohibition strict upon themselves. This has the ruling of an oath, because the intention behind this vow is not to draw near to Allah, but rather to restrain the self from this thing. So it follows the course of an oath, which is dissolved by an expiation. If one vows to do a thing, or not to do a thing, or to do it, and does not fulfill his vow, then an oath expiation is obligatory upon him. If he violates the thing he committed to, then an oath expiation is obligatory upon him, because the intention behind it is not worship, but rather to restrain himself or bind himself to something.