The 198th mitzvah is that we are commanded1 to charge interest to a non-Jew and only then lend him money, in order that we not assist him nor give him rest. Rather we should cause him [financial] loss, even with the kind of interest that we are forbidden from taking from a Jew.

The source of this commandment is G‑d's statement2 (exalted be He), "You shall take interest from a non-Jew." The Oral Tradition explains that this does not only give permission, but is a command, as stated in the Sifri: "The phrase 'You shall take interest from a non-Jew' constitutes a positive commandment. The phrase 'You shall not take interest from your brother' constitutes a prohibition."

This commandment also has rabbinically ordained conditions, as explained in tractate Bava Metzia.3