Is the salary received by the teaching assistant from the state permissible or forbidden, knowing that he sometimes worked and sometimes was absent due to unstable working conditions? Is his performing some work for free at the college sufficient to compensate for the salary he received?

The demonstrator (معيد) is obligated to adhere to the regulations and whatever the official in charge (المسؤول) decides regarding attendance and work. However, it is common that the demonstrator's work does not require a specific fixed schedule; rather, attendance is based on the needs of the work and the determination of the official. Therefore, there is no sin (حرج) in what he did by not attending when there was no obligation to do so and no work was available. Nor is there any sin upon him for the salary he received for that period. It is advised to focus on work, perfect it, and counsel the students.