“It’s possible, though, that I received the money,” acknowledged Moshe.
“In a case that neither the lender nor the borrower remembers whether a debt was repaid, the borrower has no legal obligation to pay,” said Rabbi Dayan. “There is a dispute between the authorities whether there is a moral obligation to pay, or at least compromise with, the other party. Thus, at most, Aharon should pay something as a moral obligation.” (See C.M. Taz 75:10; Shach 75:65; Pischei Teshvuah 75:21).”
“So where does that leave us?” asked Aharon.
“The money should be given to Reuven, since almost definitely it was recently placed there,” answered Rabbi Dayan. “However, since there is a slight possibility the money was left by Aharon and he is currently in possession of it, he can retain some of the money, let’s say $20, to appease Moshe, and Shimon should fill in that difference to Reuven.”