All perfect praise be to Allaah, The Lord of the Worlds. I testify that there is none worthy of worship except Allaah, and that Muhammad is His slave and Messenger. We ask Allaah to exalt his mention as well as that of his family and all his companions.
There is no harm to specialize in commercial banking with the intention of knowing the method of running these banks so that you may benefit theoretically from them with the object of setting up an Islamic bank that does not deal with interest and usury. Rather, you will be rewarded for this intention, Inshaa' Allaah. However, it is not permissible for you to work in banks that deal with usury and interest because if you do so, you are helping them in sin. Allaah says (which means): {Help you one another in virtue, righteousness and piety but do not help one another in sin and transgression. And fear Allaah. Verily, Allaah is Severe in punishment.}[Qur'an 5:2].
Nevertheless, you may set up an Islamic bank by cooperating with people who have the same qualities, objectives and religious zeal like you in inviting righteous rich people to help you establish such a bank. We ask Allaah to enable you to do whatever He likes and He is pleased with.
Allaah knows best.