On this daf, we find a case of a thief who returned what he stole.
One kind yungerman was on line at a grocery store when the middle-aged man behind him began frantically checking his pockets. “I cannot believe I forgot my wallet with my checkbook and credit cards at home!” the man said. He turned to the others on line with him. “Could someone please lay out three hundred shekels and leave me your address so that I can deal with the debt immediately?”
The yungerman readily agreed and paid the bill in cash, taking a document attesting to the loan and leaving his phone number and address with the thankful man.
A week passed and then another, but there was no sign of the borrower. After a month of checking his mailbox, the yungerman understood that the man was most likely dishonest and had meant to steal the money without returning it. He took out the loan document and ripped it up. “Master of the world,” he said, “I completely forgive this unscrupulous man and I ask You to forgive my spiritual debts in return!”
A few days later, he was shopping in a different area when he noticed the man behind him start checking his pockets for his wallet. “I can’t believe I forgot my wallet with my credit cards and checkbook at home!” It was the very same man. He turned to the yungerman and said, “Can you please advance me the money for my groceries and I will take your address and pay for them immediately after I get home?”
“I guess you do not recognize me,” shot back the yungerman. “You pulled this shtick on me over a month ago and never bothered to contact me. You took three hundred shekels from me then and I can’t think of any reason to refrain from calling the police about it.”
The suddenly frightened man immediately pulled a wad of cash out his pocket and gave the yungerman three hundred shekels.
Now the yungerman wondered if he could keep the money. Even if this was permitted, maybe it would cancel his prayer.
When these questions were presented to Rav Yitzchok Zilberstein, he ruled as follows: “It is surely a mitzvah to collect the money from this thief, since he needs to understand that stealing has consequences. If one is kind here, he is liable to face much worse in the future. Those who steal will be caught and punished eventually (see Sanhedrin 7a and Rashi there). As far as your mechilah, you forgave him because you thought you would never get the money back. This kind of erroneous mechilah is not binding, as we find in the Rama in Choshen Mishpot 241:1. Furthermore, the Aruch Hashulchan rules that forgiving a loan is only binding if the borrower hears about it and has in mind to acquire the money for himself. As long as he is unaware of the forgiveness, it is meaningless.
“Your prayer was accepted, since it was sincere. You did not expect to get the money back and were willing to forgive him. Now that you caught him and extracted the money from him, however, you should definitely keep it” (Chashukei Chemed).