What is the ruling concerning a person who engages in intercourse based on a corrupt marriage contract while believing it to be lawful?

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If an individual engages in intercourse based on a corrupt marriage contract while believing it to be lawful, no sin (*ithm*) is incurred, nor is any disciplinary punishment (*adab*) required. This is because the permissibility of such a contract is a matter of subsidiary legal rulings (*masā'il al-furū'*) where disagreement exists. If a child is born from this union, paternity (*nasab*) is established for the child in this case, as in the case where they believed it unlawful.