(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."
Does the Ban on Interest Apply Only to Your Own Money
Sifrei Devarim 262:2