(Devarim 23:20) "You shall not give interest to your brother": This tells me only of the borrower (that he should not give interest.) Whence do I derive (the same for) the lender (that he should not take interest)? From (Vayikra 25:36) "You shall not take from him interest."
(Vayikra 25:37: "Your money you shall not give him on interest, and on increase you shall not give your food."): From "your money," I derive: your money, but not that of others (i.e., gentiles); "your food," but not that of others. — But perhaps (the inference should be) "your money," but not that of ma'aser (the tithe); "your food," but not that of beasts! — (No, for "interest of money" (Devarim, Ibid.) includes money of ma'aser (as interdicted); "interest of food" includes food of beasts. This tells me only of interest of money and interest of food (as interdicted). Whence do I derive the same for any kind of interest? From (Ibid.) "interest of anything that can be (construed as) interest."
R. Shimon says: Whence is it derived that he (the lender) should not tell him (the borrower): Go and greet that man, or: Find out if that man has come from his place? From "interest of any thing ("devar," like "dibbur" [speech]).