How can atonement be made for oaths that were not fulfilled due to obsessive-compulsive disorder (OCD) regarding purity and prayer, given that the number of times the oaths were broken is unknown?

If the oath or its breach is due to obsessive doubts (waswasah), then no expiation (kaffarah) is required, because a person afflicted with waswasah is considered like someone acting under duress. However, if the oath and its breach were made by choice, then for every oath that was broken, an expiation is due. If the number of oaths is unknown, one should investigate and act upon what brings certainty or a strong presumption (ghalabat al-dhann) of absolving oneself. The Hanbalis hold that a single expiation suffices for all oaths, and it is permissible for a person afflicted with waswasah to adopt this view.