Would the father's 'Umrah be accepted if its expenses were covered by money from his son, who works in a usurious bank?

There is a difference between the validity of an act of worship and its acceptance; acceptance is an unseen matter. The majority of scholars hold that performing Hajj with unlawfully acquired money is valid and suffices, despite the sin incurred, arguing that the prohibition is due to a reason external to the acts of Hajj themselves. However, Imam Ahmad is of the view that it does not suffice. Money earned from working in an interest-based bank is ill-gotten for the one who earns it, but it is not unlawful for someone who receives it through a permissible means, such as a gift to a parent.