Is expiation (kaffarah) obligatory for one who swore an oath that no one among the participants in a religious seminar would hear the voices of women, then her brother—who has not reached the age of eight—intentionally heard their voices?

If a person swears an oath to another concerning a matter, the intention and purpose of the one who was made to swear (the oath-taker) are referred to the one who requested the oath (the oath-requester), in accordance with the Prophet’s (peace and blessings be upon him) saying: "Your oath is according to what your companion believes you to be truthful about," and in another narration: "The oath is based on the intention of the one who requested it." If the intention of the one who requested the oath specifies the apparent meaning of the oath to a particular situation or person, then the oath-taker does not break the oath unless he contradicts that intention.

Based on this, if the intention of the women was that no one should hear their voices who is not permitted to derive pleasure from hearing them among foreign men, then a boy hearing their voices does not cause a breach of the oath. However, if their intention was that absolutely no one should hear their voices, then the general phrasing includes everyone, and in this case, it is necessary to offer an expiation for breaking the oath.