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]).
(Devarim 23:21) "To the stranger shall you give interest, but to your brother shall you not give interest": "to the stranger shall you give interest" — a positive commandment; "but to your brother shall you not give interest — a negative commandment.