What is the ruling of Islamic law on dealing with a mother's insistence that her son take out an interest-bearing loan to buy a house and a car, even though he knows it is forbidden, and her threatening him with anger and abandonment if he does not comply?

Obedience to parents is obligatory in matters that do not involve disobedience (to Allah). If Allah’s command contradicts a parental command that entails going against Allah’s command, then Allah’s command must be prioritized, for the Prophet, peace and blessings be upon him, said: "There is no obedience to a creature in disobedience to the Creator." Accordingly, borrowing with interest (riba) is forbidden, and you must inform your mother of its prohibition gently and kindly, while trying to convince her that ill-gotten wealth has no blessing in it.