Is it permissible for me to take the money my colleague gave me in exchange for help he received, knowing that I had told him that the two thousand riyals were not mine?

If the 2000 Riyals are taken by the bank employee in exchange for their influence to facilitate a loan for someone who meets its conditions, this is permissible according to some jurists. However, if this is part of the employee's job, but they refuse to perform it except for a financial consideration, then this is a prohibited bribe. If they achieve the lending through lying or falsification, their action is prohibited, and the money they take is forbidden.

As for the 2000 Riyals, if you were to take them yourself, and you lied to your friend that they were for the bank employee, this is a prohibited lie, and the money is not lawful for you. You must repent and return the money to its owner. There is no harm in you hinting to him without explicitly lying. If he gives you something from it, there is no harm in that.

It is a condition for this loan that it be a good loan (Qard Hasan) that does not involve interest or late fees; otherwise, it would be an usurious loan (Riba-based) which is impermissible to take or to mediate.