Is it permissible to buy a house with money from an interest-based loan taken by the father, and is repaying the price to the father considered aiding in usury?

The Fatwa's Essence: The sin of borrowing with interest (riba) is attached to the borrower's conscience, not to the money itself. What your father did by borrowing with interest is forbidden and considered among the major sins, and he must repent. As for you, there is no sin upon you. You are permitted to buy the house from your father with monthly installments, and it does not harm you that it was built with a usurious loan, because the sin of the loan is attached to the borrower's conscience, not to the house.