Is it permissible for me to give a gift to a manager who nominated me to carry out development work on water projects, knowing the Prophet's (peace be upon him) saying: "Whoever intercedes with an intercession and is then given a gift for it, and accepts it, has indeed entered a great door from the doors of usury"?

The Hadith (definition) "Whoever intercedes for his brother with an intercession, and he gifts him a present for it, and he accepts it, then he has approached a great door from the doors of usury (riba)" has been weakened by some scholars and authenticated (declared hasan (definition)) by others. Assuming it is hasan, it is forbidden for one who intercedes for another to accept a gift if the intercession was for an obligatory matter or a forbidden one. However, in permissible matters, it is more virtuous not to accept the gift and to intend the pleasure of Allah. Calling the gift usury is metaphorical, due to the similarity between them, as usury is an increase in wealth without compensation. Therefore, it is permissible to give a gift to this person, but it is more virtuous for him to decline the gift and seek reward from Allah.