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.
It is safer for your religion to leave teaching the son of a banker since his wealth is mostly mixed with Riba (interest and usury) for the Prophet said: “What is lawful is clear and what is forbidden is clear, and in between them there are some things that are doubtful, which most people do not know –if they are lawful or forbidden. Thus, whoever avoids what is doubtful, safeguards his religion and honor, but one who engages in what is doubtful, falls in what is forbidden. The example of this is like the shepherd who grazes his herd in the vicinity of an exclusively reserved pasture but it is always apprehensive that some of his animals might get into the pasture. Every king has a reserved pasture and the reserved pasture of Allah is what He has forbidden.” [Al-Bukhari and Muslim]
Besides, Al-Hassan ibn ‘Ali, may Allah be pleased with him, narrated that the Prophet said: “Leave that which is doubtful and adopt that which is not doubtful.” [An-Nassa'i and At-Tirmithi]
Ibn Qudamah said in his book Al-Mughni concerning dealing with one who deals in Riba: “If a person buys from another person whose wealth is a mixture of what is lawful and what is forbidden, like an unjust ruler and a person who deals in Riba, then one's dealing is lawful if one is sure that he deals with the lawful portion of wealth of the other person, and vice versa. But, if one does not know that, then we dislike such dealing for it is possible to be forbidden, and such dealing is valid since it also might be lawful and this is the doubtful thing. Then, the more forbidden is the other person's wealth, the more it will be forbidden to deal with him, and vice versa.”
Thus, it is safer to give up such a work and better to avoid difference among scholars and to show hate to this banker's business and those who like him.
Allah Knows best.