Prohibitions and oaths of abstinence are treated as oaths.

The Shaykh : Furthermore, prohibitions and oaths of abstinence are treated as oaths, and their ruling is the same as that of an oath. If you say, "It is forbidden for me to wear this garment," it is the same as saying, "By Allah, I will not wear this garment." Accordingly, if you wear the garment, you must pay the expiation for an oath. The evidence for this is the statement of Allah, Blessed and Exalted is He, to the Prophet (peace and blessings be upon him): Allah called a prohibition an oath. Is a prohibition considered an oath in every case, whether regarding clothing, food, visiting, or anything else? Or is there a distinction between a wife and others in this regard? There is scholarly disagreement on this point.