Negative commandment · Lo Ta’aseh #237 of 613
That we not give a hand between the borrower and the creditor with interest
שלא להשית יד בין לווה ומלווה בריבית, ולא להיות ערב, ולא עד, ולא לכתוב שטר ביניהם
The verse · Shemot 22:24
אִם־כֶּסֶף תַּלְוֶה אֶת־עַמִּי אֶת־הֶעָנִי עִמָּךְ לֹא־תִהְיֶה לוֹ כְּנֹשֶׁה לֹא־תְשִׂימוּן עָלָיו נֶשֶׁךְ
“If thou lend money to any of my people that is poor by thee, thou shalt not be to him as a creditor, neither shall you lay upon him interest.”
The Rambam’s words
Not to intermediate between the borrower and lender when interest is involved, not to act as a guarantor or a witness [to such a loan], nor to draw up a contract for it, as [Exodus 22:24] states: "Do not charge him interest."
שלא להשית יד בין לווה ומלווה בריבית, ולא להיות ערב, ולא עד, ולא לכתוב שטר ביניהם, שנאמר "לא תשימון עליו, נשך" (שמות כב,כד).
Why · Sefer HaChinuch #68
That we not give a hand between the borrower and the creditor with interest
“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.”
Who & when
“And [it] is practiced in every place and at all times by males and females.”
Where in the Mishneh Torah
Hilchot Creditor and Debtor הלכות מלווה ולווה