impairs monotheism is graver than one that results in an act of disobedience. If Allah has prescribed expiation to rectify and repair the harm that breaking an oath causes to monotheism and the like, then it is all the more fitting and appropriate that He should prescribe it to rectify the harm that breaking an oath causes to obedience.

We also say that the legal effect of an oath formula is the same as that of a conditional formula. A vow is a kind of oath, and every vow is an oath. Thus, a person’s statement, “I owe it to Allah to do this,” is equivalent to saying, “I swear by Allah that I will certainly do this.” Both statements entail binding oneself to perform the act by invoking Allah. The evidence for this is the Prophet’s statement (may Allah bless him and grant him peace):

“A vow is an oath.”

Thus, saying, “If I do such-and-such, I am obliged to perform Hajj for Allah,” is equivalent to saying, “If I do such-and-such, then, by Allah, I will certainly perform Hajj.” A consistent application of this principle entails that, if someone swears to perform a righteous deed, he must perform it and may not discharge his obligation through expiation, since his oath to perform it constitutes a vow to do so.

Likewise, a consistent application of this principle entails that, if someone vows to commit a sin or perform a permissible act, he has sworn to do it, just as though he had said, “By Allah, I will certainly do such-and-such.” If he swears by Allah to commit a sin or perform a permissible act, expiation for an oath becomes obligatory upon him; the same therefore applies if he says, “I owe it to Allah to do such-and-such.” Some jurists, both of our school and of others, distinguish between these two cases.

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As for oaths involving “divorce and manumission” in contention or anger—where the intention is to urge an action, prevent it, affirm a statement, or deny it—an example is saying, “Divorce shall be binding upon me: I will certainly do