What should a dutiful son do when his disobedient and corrupt father asks him for financial assistance, knowing that his father is a liar and that there is a possibility he will use this money to disobey God?

It is recommended to be gentle with the parent, advise him kindly, and not despair of his guidance. Accompany him with kindness and benevolence, even if he mistreats you, and strive to invite him to the truth. Among the acts of filial piety is to be good to them financially, for they have a right to maintenance. However, it is not permissible to give him money if you are certain or highly suspect that he will use it in disobedience to Allah. Rather, it is an act of piety to prevent him from doing so.