What is the ruling on the salary paid to a person for three years without work, and must it be returned, and is donating it to public entities such as for building schools and mosques rewarded?

Salary has three considerations: First: If it is from a private institution, and its owner is responsible for the work, then the the salary is lawful for you because it is a gift from him. Second: If it is from a private institution, and the person in charge of it is not its owner, then you must return it to the institution because the Prophet, peace and blessings be upon him, said: "The wealth of a Muslim is not lawful except with his willing consent." Third: If it is from state institutions, then it is not lawful for you unless you perform the duty for which you are paid, and state wealth is shared by all its citizens. It can be returned to the public treasury if those in charge are just; otherwise, it should be spent on general Muslim welfare, or given as charity to the poor.