What should one do who comes to know about their father's customary marriage?

If an 'urfi marriage (customary marriage) is intended as a secret marriage without a guardian (wali), then it is invalid. However, if it fulfills the conditions and pillars of marriage, such as the guardian, witnesses, offer, and acceptance, then it is legally valid, even if it is not registered with a judge. Whoever knows that their father contracted an invalid marriage must explain the ruling of the Shari'ah to him and enjoin what is right and forbid what is wrong. If the marriage is valid but unregistered, then he should be advised to register it to preserve rights and prevent corruption, while noting that enjoining a parent differs from enjoining others.