The expiation falls upon the one who swears the oath
Question: A man swore an oath binding another person not to carry out a certain action, yet that second person went ahead and did it. Upon whom does the expiation for this oath fall?
Answer: The expiation is due from the oath-taker. If someone swears that another must not do something—or must do it—and the sworn-upon matter is violated, the obligation to offer expiation rests with the one who pronounced the oath.
Question: If the person addressed by the oath knowingly acts in defiance of it, is he sinful?
Answer: The Messenger of Allah ﷺ commanded that an oath be honored. Therefore, the person addressed by the oath should comply with what the oath-taker requested. If he goes against it, he has acted contrary to what is proper and preferable.
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Question: My wife told me that if I allowed my brother to enter our home without her knowledge, she would become forbidden to me. It happened that this brother came in and I did not inform her. In this situation, does she in fact become forbidden to me?
Answer: If her intent was to prevent that person from entering the house until she knew and granted permission, and you brought him in without her knowledge, then she has broken what she swore. This is treated as an oath, so she must make the expiation for an oath: freeing a slave; or feeding ten needy people, each one receiving half a sāʿ of staple food; or clothing ten needy people, one garment each. If she cannot manage any of these three options, she must fast for three days. That will serve as the expiation for her oath—namely, her declaration that you would be forbidden to her.