What is the ruling on a doctor taking for himself one-third of what he earns from examinations conducted after official working hours, knowing that this is the prevailing custom and with the knowledge of officials? And if this money must be returned, how is that to be done?

The worker must return what exceeds one-third, which is his rightful share of the money he took. This money should be returned to the health administration or the state treasury, and not to the people who paid it. This is because the custom that workers have adopted, of taking all the money, is a form of deception and does not make lawful what is unlawful, as custom is only considered if it does not contradict the explicit condition of the contracting parties.