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A husband may level an accusation of adultery against his wife when he knows she has committed the act or when he has a firmly-grounded suspicion—for instance, when widespread talk links her to Zayd and he has additional evidence, such as having seen them alone together. If she gives birth to a child and he is certain the child is not his, he must disclaim paternity. Such certainty exists only in three cases: (1) he has not had intercourse with her, (2) she delivers in less than six months from their last intercourse, or (3) she delivers after more than four years. If she delivers between those two limits and he has not observed a menstrual period of istibrāʾ (the waiting period to ensure the womb is clear), it is unlawful for him to repudiate the child. On the sounder view, he may disclaim paternity when she delivers more than six months after the istibrāʾ. If he had intercourse but practiced withdrawal (ʿazl), it is, according to the sounder opinion, forbidden to disclaim. Even when he is certain of her adultery, if the child could plausibly be his as well as the product of adultery, it is prohibited—on the correct position—for him to repudiate the child, accuse her, or initiate liʿān.

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The formula of liʿān is that the husband says four times: “I testify by Allah that I am surely among the truthful regarding the charge of adultery I have levelled against this woman.” If she is absent, he identifies her by name and lineage. The fifth time he adds: “May the curse of Allah be upon me if I am among the liars concerning what I have alleged against her of adultery.” When he is also disowning a child he inserts: “and that the child she has borne—or this child—is the result of adultery and not mine.”
She then says four times: “I testify by Allah that he is indeed lying in the accusation of adultery he has made against me,” and the fifth time: “May the wrath of Allah be upon me if he is telling the truth in this.” If either spouse substitutes the word “testify” with “swear,” replaces “curse” with “wrath” or vice versa, or utters the final formula before completing the four testimonies, the liʿān is invalid according to the sounder opinion.
A valid liʿān further requires the judge’s authorization, his dictation of the precise words, and that the wife’s imprecation follow the husband’s. A mute person performs liʿān by intelligible signs or by writing. Performing it in a non-Arabic language is valid, though there is a differing opinion when the person knows Arabic. The oath is intensified by its timing, namely when it is performed after the ʿAsr prayer.