First of all, what he did was wrong because he didn't follow the order of his parent's but now that he already committed the mistake, I think it will now be easy for him to commit another mistake which is to lie, just in case his parents find out about the money. Im sure there must be other profitable activity that is allowed in his country like investing or trading. He can just say that he got the money from those sources. There might still be people who can feel guilty right after making one mistake and they will confess it right away. They think this will lessen the punishment that they will be getting.
Sure it was a mistake but everything had happened and he had brought the money. But if he's not telling the truth, he's already lying but maybe he can use the money to set up a new business. He can also say that his business started small and is trying to grow his business. He can also say that he borrowed some amount to trade or invest and made a big profit. Again, everything had happened and it was up to him what he wanted to tell his parents. Let's just hope his parents take it and remind him that this is for the last time.