What are the prescribed requirements and procedures for the mutual imprecation (Li'an) between spouses?

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The Li'an is not valid unless conducted in the presence of the judge (Hākim) or their appointed representative. This is the established position of Shafi'i scholars, evidenced by the command of the Prophet, peace be upon him, to Hilāl ibn Umayyah to summon his wife for mutual imprecation. Whether Li'an is considered an oath or testimony, the presence of the judge is a mandatory condition for both. If the spouses agree to perform Li'an without the judge, it is invalid because Li'an is founded upon solemnity and emphasis, thus requiring a judge, similar to legal punishments (Hudūd). This applies whether the spouses are free or enslaved, according to the apparent view of Al-Kharqi. The husband initiates by testifying four times, saying, "I bear witness before Allah that she has committed adultery," pointing to her or naming and describing her if she is absent. After the fourth time, he is stopped and warned, "Fear Allah, for this is the statement that necessitates [consequences]. The punishment of the world is lighter than the punishment of the Hereafter." If he insists on completing it, he must say, "And the curse of Allah be upon me if I am among those who are lying regarding what I accused her of adultery." The wife then replies four times, "I bear witness before Allah that he is lying." She is then stopped at the fifth time and warned similarly. If she refuses to stop, she must say, "And the wrath of Allah be upon me if he is among those who are truthful in what he accused me of adultery."