What is the ruling on one who supervises a project for his brother, friend, or relative, then takes a wage for that work without prior agreement and conceals it?

If someone works for another at their request without an agreement on wages, then if he usually works for pay, he is entitled to the customary wage (ujrat al-mithl). But if he usually works gratuitously, then he is entitled to nothing and is considered a volunteer, unless the other person gives him something willingly.