Assalaam alaykum dear scholars. I have a question about my father's occupation. He works as an accountant in a petroleum company. He completes his job everyday except for some work that can be delayed, such as filing. He leaves the filing to do it on saturday, which is extra hours, not official work hours, in order to get overtime money. For the company, the fact that he postpones that work until Saturday does not affect it; it is not urgent. However, by doing so, he works on Saturdays to get overtime salary. On Saturdays, there is no work, except if you have remaining work from the previous days, and then one goes and works on that. My question is whether it is halal for my father to earn that overtime money or not. I advised him to leave it since it looks suspicious, but i want your opinion as well; thank you in advance.

All perfect praise be to Allaah, The Lord of the Worlds. I testify that there is none worthy of worship except Allaah and that Muhammad, sallallaahu ʻalayhi wa sallam, is His slave and Messenger. 

The calculation of overtime work hours and their wages is determined by the consent of the employer and according to the terms of agreement between the employer and employee.

Hence, if the regulations of the company state that the overtime hours are especially for carrying out the unfinished duties that the employee has no sufficient time to finish during regular working hours, then the employee must abide by that. In this case, you father does not have the right to violate these regulations by deliberately delaying some of the work duties assigned to him during the week to Saturdays while being able to perform them earlier so that they would be counted as overtime work hours and he can get the overtime wages accordingly. Verily, this act constitutes a deceitful attempt to unjustly take money from the company, which is prohibited. Allaah, The Exalted, says (what means): {And do not consume one another's wealth unjustly...} [Quran 2:188]

Hence, the money that your father has received for the overtime work hours is not lawful for him, and it is incumbent on him to clear himself of his liability from it by either returning it to the company or by seeking their pardon.

Allaah knows best.