Am I obligated to fulfill an oath if I don't remember whether I made it or not?

If you swear by Allah Almighty to a person that you will do something if he does something else, and that person does what was mentioned, then you must fulfill your oath. Otherwise, you become a breaker of your oath (hanith) and atonement becomes obligatory upon you. And whoever swears to do something and does not do it, atonement becomes obligatory upon him, even if he does not remember the exact thing he swore about. The important thing is that he knows he broke his oath. The atonement for an oath (kaffarat al-yamin (definition)) is feeding ten needy persons with the average of what one feeds his own family, or clothing them, or freeing a slave. Whoever does not find these options, then he must fast for three days. This is in accordance with the Almighty's saying: "So its atonement is the feeding of ten needy persons from the average of what you feed your [own] families, or clothing them, or the freeing of a slave. But whoever finds none, then a fast of three days. That is the atonement for your oaths when you have sworn. And guard your oaths. Thus does Allah make clear to you His verses that you may be grateful" (Al-Ma'idah: 89).