Is it permissible for a father to keep an extra $300 resulting from an accounting error at the university, knowing that university regulations stipulate that any surplus be registered in its name for whoever claims it? And is this money considered unlawful? What is the ruling on eating, drinking, and clothing oneself from it? What should the son do if the father does not heed his advice? Should this money be treated as a found item or according to university regulations?

Your father is not permitted to take the aforementioned money for himself, because he is an employee bound by the regulations of the university, which obligate him to return those funds to the university so that it may return them to their rightful owners. He must adhere to this. You should advise your father in a polite and gentle manner not to benefit from that money. As for your eating and drinking from his money, there is no harm in it, because his money becomes mixed if he takes those funds which are not permissible for him, and eating from food of mixed wealth is permissible.