Buying and Selling: Taking Interest from a Family Member or a Disbeliever

Practical Laws of Islam as per the teachings of Ayatullah Sistani

Ruling 2088

A father and his child, and a wife and husband, can take interest from one another. Similarly, a Muslim can take interest from a disbeliever (kāfir) who is not under the protection of Islam. However, an interest-based transaction with a disbeliever who is under the protection of Islam is unlawful. Of course, after the transaction has taken place, one can take more from him if giving interest is permitted in his religion.

-Ayatullah Sistani, Practical Laws of Islam, Buying and Selling