What is li'an?

Li'an is what transpires between a husband and wife, consisting of testimonies and emphatic oaths, when the husband accuses his wife of adultery without proof, or denies the paternity of a child born to her. It is resorted to through the process of mutual imprecation (mula'anah) with the formula mentioned in Surat An-Nur. If li'an takes place, permanent separation occurs between them, the prescribed punishment (hadd) is averted from both, and the lineage of the child concerned in the li'an is disowned.