Rashi on Deuteronomy 23:20/רש"י על דברים כ״ג:כ׳

1לא תשיך implies a prohibition addressed to the borrower that he should not pay interest to the creditor (cf. Sifrei Devarim 262:1; Bava Metzia 75b) [and afterwards (Leviticus 25:37) follows the prohibition addressed to the creditor, “thou shalt not give him thy money upon interest”].