How can we explain the harm of usury to non-Muslims, and what is the alternative? Is it permissible to use the father's credit card in cases of urgent necessity, knowing that the father is not convinced of the prohibition of usury and is seeking to establish a commercial business?

Usury (riba) is forbidden in Islam, and it has economic and social harms. Usurious banks compel merchants to raise prices, and lead to the stagnation of capital and unemployment. Banks can achieve profits through legitimate means such as Mudarabah (profit-sharing), Istisna' (manufacturing contract), and Murabahah (cost-plus financing).

If a credit card is covered (i.e., has a sufficient balance), there is no objection to it. However, if it is uncovered, any amount exceeding the balance is considered a usurious loan.

The father should be advised kindly if he deals with usury, and its danger should be explained to him. The sin of usury falls upon the borrower. The borrowed money is owned by the father, and his children are permitted to benefit from it. However, the father should be advised and helped to seek lawful earnings.