Is it permissible for an employee to receive payment for overtime hours that he did not work, knowing that he reports to duty before the official time without being assigned to do so by the ministry?

If the institution's regulations permit taking the increase, or if the competent authority authorizes it, then there is no objection to receiving it and benefiting from it. However, if the regulations do not stipulate this and the competent authority does not authorize it, then it is not permissible to take this increase, because it is payment without work. And continuous presence before the official time does not change the ruling.