The Weisers had moved across town some years back but remained friendly with their former neighbors, the Landers. The families arranged to go out together to a restaurant.
At the end of the meal, the waiter brought the bill for each family. The Weisers’ bill came to $480.
Mr. Weiser pulled out his wallet but couldn’t find his credit card. “I don’t believe it!” he exclaimed. “I accidentally left my credit card on the desk last night after paying some bills.”
“I didn’t bring my pocketbook,” Mrs. Weiser added. “So I don’t have mine, either.”
“No problem,” said Mr. Lander. “I’ll charge the bill to my card and you can pay me back when it’s convenient.”
“We would appreciate that,” said Mr. Weiser.
Mr. Lander told the waiter to charge both bills to his card.
The following week, Mr. Weiser stopped off at Mr. Lander’s house to repay him for laying out the money. He handed Mr. Lander an envelope.
“Thank you very much,” said Mr. Lander. “It was $480. Is the right amount in here?”
“Yes,” said Mr. Weiser. “I counted the money.”
After Mr. Weiser left, Mr. Lander opened the envelope. He counted the money and found $600. There were five one-hundred dollar bills and five twenties. “That’s strange,” Mr. Lander said. “He only owed $480.”
“You should call Mr. Weiser and return the extra to him,” said Mrs. Lander. “He clearly made a mistake. He should have given four bills of each, but gave an extra one.”
“Do you think he would make such a mistake?” asked Mr. Lander.
“It’s possible,” replied Mrs. Lander. “Sometimes bills get stuck or a person makes an error in his count.”
“It seems strange,” said Mr. Lander. “I asked Mr. Weiser whether it was the right amount, and he said that he counted the money.”
Mr. Lander decided to consult Rabbi Dayan. “What should I do with the extra money?” he asked.
“You must notify Mr. Weiser and return the extra money to him,” answered Rabbi Dayan.
“Why is that?” asked Mr. Lander.
“The Gemara [B.M. 63b] teaches that when the borrower returns extra bills, we assume he counted wrong, within reason,” explained Rabbi Dayan. “A bill of the wrong denomination is also assumed to be a mistake, if the bills are somewhat similar.” (C.M. 232:2; Aruch Hashulchan 232:3; Pischei Choshen, Geneivah 11[58])
“What if it was clearly not a mistake?” asked Mr. Lander. “For example, if there were five hundred-dollar bills?”
“ln that case, you would not have to return the extra,” replied Rabbi Dayan. “The extra was clearly added intentionally. We assume that he owed you money from some other occasion or gave it as a gift.”
“Wouldn’t giving money as a gift be ribbis [interest], though?” asked Mr. Lander. “How does that help?”
“Indeed, the borrower is not allowed to add extra when he repays, even as a gift,” said Rabbi Dayan. “However, if the lender received the extra gift without realizing it, some say that he is not obligated to return it.” (Y.D. and Pischei Teshuvah 160:4)
“Why not?” asked Mr. Lander.
“The rules of returning ribbis depend on the severity of the ribbis,” replied Rabbi Dayan. “Standard, stipulated, interest for a loan – ribbis ketzutzah – which is biblically prohibited, must be returned and is enforceable in beis din. Most other forms of ribbis – avak ribbis – which are prohibited by the Sages are not enforceable, but the lender has a moral responsibility to return it.
“However, with a gift the borrower gives after repaying the loan – ribbis me’ucheres – there is not even a moral responsibility to return. Regarding extra added while repaying the loan, such as this, there is a dispute whether there is a moral responsibility to return.” (Y.D. 161:2,5; Shach 160:4; Chavos Da’as Y.D. 160:2)