They said:

Moreover, when a man likens his wife to his mother’s back or declares her forbidden to him, saying, “You are to me like my mother’s back,” or, “You are forbidden to me,” he has undertaken only a legal consequence, not an act. Nevertheless, expiation applies in this case.

They said:

Just as someone who undertakes the obligation of emancipation has the choice between accepting that obligation and offering expiation, someone who undertakes that emancipation itself should take effect likewise has a choice. He may accept its taking effect, emancipating the slave and letting him go, so that his emancipation—his release of the slave—fulfills the vow. Alternatively, he may neither emancipate him nor let him go; he does not offer expiation in fulfillment of the vow, but rather owes expiation.

This is like someone who says, “If I do such-and-such, this wealth is charity,” or, “This camel is a sacrificial offering,” and then breaks his oath. He has the choice between giving the wealth in charity and sending the camel as a sacrificial offering—thereby accepting the consequences of its being charity or a sacrificial offering—and offering expiation while retaining the wealth and the sacrificial animal rather than sending it away.

If, however, he undertakes something forbidden, such as saying, “If I do such-and-such, I am bound to desecrate a copy of the Quran,” or the like, then, by scholarly agreement, he is not permitted to do so. Whether expiation is obligatory is subject to the disagreement mentioned earlier.

The same applies if he undertakes a legal consequence that he is not permitted to undertake, as when he says, “If I do such-and-such, I am a Jew or a Christian.” He is not permitted to commit himself to disbelief in any way whatsoever. If he intended that, he would become a disbeliever by that very intention.

The point is that neither in revealed law nor in customary usage is there any distinction between undertaking a legal consequence that obliges him to perform an act, which in turn entails another legal consequence requiring or prohibiting an act, and undertaking the legal consequence requiring or prohibiting that act.

Undertaking the obligation to perform the act that entails that legal consequence is illustrated by saying, “Then I am bound to divorce or emancipate.” For he