—for the Messenger of Allah (peace and blessings be upon him) said: “Whoever introduces into this affair of ours something that does not belong to it, it is rejected.” A person should also avoid multiplying his oaths, for this is the purport of Allah’s words, “and safeguard your oaths” (Quran 5:89), according to some exegetes who explain the verse as meaning: do not swear by Allah excessively.

When you do swear, it is recommended that you bind the oath to the divine will by saying, “By Allah, if Allah wills.” In this you reap two great benefits. First, the matter you swore about will, by Allah’s leave, become easier to accomplish. Second, should you break the oath, no expiation is due; whoever swears and adds “if Allah wills” is not considered to have broken his oath even if he acts contrary to it.

Expiation is required only for an oath that concerns a future act. An oath regarding something in the past carries no expiation, though the swearer is sinful if he lies and blameless if he tells the truth. For example, if someone says, “By Allah, I did not do such-and-such,” no expiation is due whether he is truthful or lying. If he is truthful—that he really did not do it—he commits no sin; if he is lying, having in fact done it, he is sinful.

The oath that obliges expiation, then, is one about a future matter. If you swear, “By Allah, I will not do such-and-such,” we say: should you go ahead and do it, expiation becomes obligatory; if you refrain, no expiation is required. “By Allah, I will not do such-and-such”—this is an oath