Is the amount that will be received in exchange for working at a usurious loan association considered permissible or forbidden, knowing that the work was completed before the association began its activities?

It is not permissible to work for an association that deals with interest-based lending, because it is usury (riba), which Allah has warned against, as He states: "O you who have believed, fear Allah and give up what remains [due to you] of interest, if you should be believers. And if you do not, then be informed of a war [against you] from Allah and His Messenger. But if you repent, you may have your principal - [thus] you do no wrong, nor are you wronged." It also involves aiding in sin and aggression, as Allah says: "And cooperate in righteousness and piety, but do not cooperate in sin and aggression." The Prophet (peace and blessings be upon him) cursed the one who consumes riba, the one who feeds it, its scribe, and its two witnesses. It is not permissible to benefit from the salary earned from this work. Whatever you have taken from it must be disposed of by spending it on general Muslim welfare or giving it to the poor.