Is a retirement salary acquired from prior work in a banking institution permissible or impermissible?

Working in banks and usurious institutions is unlawful (haram (definition)) because it involves assisting in sin, and the salary an employee receives from such work is unlawful. Similarly, the pension and end-of-service gratuity related to that work are also unlawful. It is obligatory for anyone who was working in this field to repent to Allah and to dispose of these amounts by spending them on the general welfare of Muslims, such as distributing them to the poor, the needy, and the indigent. If the repentant person is poor and in need, they may take from it what suffices their needs.