Is it permissible to work for a company whose products are halal, but whose capital is mixed with usurious companies and banks?

Usury is a grave sin, and Allah has declared war on those who engage in it. It is not permissible for a Muslim to work in an institution that deals with usury, due to the cooperation in sin and transgression involved. If the institution does not practice usury but usurious banks contribute to its capital, it is preferable to avoid working with it if other options are available. However, working there is not forbidden, as it is like possessing unlawful wealth mixed with lawful wealth.