Is a person who vows not to disobey (God) and then disobeys subject to two sins? What is the ruling on one who makes a vow not related to abandoning a sin and then doubts its existence? And what is the expiation for one who swears to do certain things but then does not do them?

Scholars differ regarding vows to abandon sin. Some are of the opinion that such a vow is binding and that violating it increases sin. Others—and they are the majority—believe that it is not binding because abandoning sin is an obligation by the very essence of Islamic law, and that such a vow is vain and does not increase sin by acting contrary to it.

As for what you doubt concerning oaths or vows, the default is that they were not uttered by you, and nothing is binding upon you.

If you swore many oaths and do not recall their number, then, according to the majority of scholars, you must make an effort to estimate them and offer expiation for each oath. This is more cautious and more absolving of responsibility. Hanbali jurists are of the view that oaths whose obligations are of the same kind overlap, and a single expiation suffices for them.