Is the son who spent his father's money on something illicit, without his father's knowledge, obligated to return this money to his father after he starts working, and how is the amount estimated if restitution is obligatory?

If the son takes money from his father with his permission, he has owned it. He must repent if he spends it on something unlawful, and he is not obliged to return it to his father. However, if he steals it, he must return it to him or seek his forgiveness. If he does not know the exact amount, he must estimate the amount that he believes most likely covers the right or exceeds it.