Negative commandment · Lo Ta’aseh #236 of 613
Not to borrow with interest
שלא ללוות בריבית
The verse · Devarim 23:20
לֹא־תַשִּׁיךְ לְאָחִיךָ נֶשֶׁךְ כֶּסֶף נֶשֶׁךְ אֹכֶל נֶשֶׁךְ כׇּל־דָּבָר אֲשֶׁר יִשָּׁךְ
“Thou shalt not give interest to thy brother; interest of money, interest of foodstuff, interest of anything that is lent upon interest;”
The Rambam’s words
Not to borrow with interest, as [inferred from Deuteronomy 23:20, which] states: "Do not take interest from your brother." According to the oral tradition, this verse is interpreted as a prohibition, forbidding a borrower from paying interest to a lender.
שלא ללוות בריבית, שנאמר "לא תשיך לאחיך" (דברים כג,כ); כך למדו מפי השמועה, שזו אזהרה ללווה שלא יינשך למלווה.
Why · Sefer HaChinuch #572
That the borrower not give interest to an Israelite
“It is from the roots of this commandment [that it is] because the good G-d desired the settlement of His people which He chose. And therefore He commanded to remove the obstacle from their path, that one should not swallow up the wealth of his friend without his [even] feeling it, until he finds his house empty of all good.”
Where in the Mishneh Torah
Hilchot Creditor and Debtor הלכות מלווה ולווה