Is it permissible for a civil engineer in a government department to accept a commission for nominating contractors to entities unrelated to his institution, knowing that nominating contractors is not part of his core duties?

Intercession is mediating for others to bring about a benefit or ward off harm. It is a righteous deed for which a person is rewarded if it is for good. As for the ruling on taking payment or a gift in exchange for intercession, scholars have differed on it. One group has prohibited it, relying on the hadith: "Whoever intercedes for his brother with an intercession, and then he is given a gift for it, and he accepts it, then he has approached a great door from the doors of usury." They believe that intercession is a righteous deed for which one is rewarded by Allah, so no payment should be taken for it. Another group has permitted taking payment or a gift for intercession if it was not obligatory upon the intercessor, interpreting the aforementioned hadith as referring to obligatory or forbidden intercession. Based on this, it is better not to take anything in return for intercession, so that you may fully reserve your reward.