Is the salary of a teacher whose work is limited to two classes per week and one supervisory day, while he spends the rest of the days merely signing in, lawful or unlawful?

If an agreement is made with the employer to teach two sessions per week and have one supervisory day, with no other work involved, then the salary is permissible. However, if the employer stipulated other tasks and these were not fulfilled, then the received salary is unlawful.