Is it permissible for a student to present a false medical excuse to postpone exams, knowing that it harms no one?

As long as the university does not permit the postponement of exams except with an excuse, it is not permissible for the student to submit an untrue medical excuse to postpone exams, for this is forbidden deception and lying, due to the Prophet (peace be upon him) saying: "Whoever cheats is not from me."