Aristotle, Nicomachean Ethics
H. Rackham, Ed.

2. [5] As a general rule then, as has been said, one ought to pay back a debt, but if the balance of nobility or urgency is on the side of employing the money for a gift, then one ought to decide in favor of the gift. For （b） there are occasions when it would be actually unfair to return the original service; as for instance when A has done B a service knowing him to be a good man, and B is called upon to return the service to A whom he believes to be a bad man. For even when A has lent B a loan, B is not always bound to lend A a loan in turn: A may have lent money to B, who is an honest man, expecting to get his money back, while B would have no hope of recovering from A, who is a rascal. If A is really a rascal, the return he asks for is not a fair one; and even if A is not a rascal, but people think¹ he is, it would not be deemed unreasonable for B to refuse.