Am I sinful for eating from my father's money, which is mixed between halal and interest from usurious banks? Will my prayers not be answered? Is it permissible for me to use the money saved from my father's allowance—which is mixed—for trade?

It is forbidden to deposit money in usurious banks, and the interest generated from it is unlawful gain for the earner. As for children, wives, and those whom one supports, it is permissible for them to consume from this money, because its unlawfulness applies only to the earner, not to those who acquire it through a permissible means such as maintenance, a gift, or inheritance. Therefore, money that is unlawful due to its earning is not unlawful for one who acquires it through a permissible means, unlike money that is unlawful in itself, such as alcohol or stolen property. Hence, there is no harm in receiving maintenance from a father even if it comes from usurious interest, for consuming it is lawful for them, and its sin is upon the father. There is no harm in trading with saved money if its saving was permissible.