Is it obligatory to return the money to the father who prevented his son from transferring his money from a usurious bank to an Islamic bank, or is that considered cooperation in sin, or is it permissible to take it without his consent?

A father may retract his gift to his child if the money is still intact and no third-party rights are attached to it. This is based on the Prophet's (peace be upon him) saying: "It is not permissible for anyone to give a gift and then retract it, except for a father regarding what he gives to his child." Four conditions are required for retracting a gift: that it remains in the son's possession and control, that no one other than the child has an interest in it, and that it has not increased in value in an inseparable manner. You bear no sin if the father deposits it in an interest-bearing bank, but you should gently advise him against it.