Bava Kamma, Chapter 10, Mishnah 3. In the previous mishnayos, the Mishnah explained the laws of yei'ush, meaning the owner's loss of hope of recovering what was stolen from him, and the law of shinui reshus, the transfer of the object to other hands, by virtue of which the new owner is permitted to keep what came into his possession even though it originally belonged to another. Our mishnah comes to discuss a case where the object is discovered in the possession of the buyer.
Reuven and Shimon are walking down the street, and Reuven recognizes his own coat on Shimon. He claims that it was stolen from him and that he never gave up hope of recovering it. Shimon, for his part, replies that he bought the coat in good faith and for full price, at a second-hand store or on a sales website. While it may have belonged to someone else before him, he does not know to whom and it is none of his business. How do we decide between the two?
The underlying principle of the mishnah:
If Reuven's claim makes a lot of sense, and there is a substantial basis to believe that the object was stolen from him and that he did not give up hope of retrieving it, Reuven will get his item back, in a manner that will be explained below. However, if the claim is not sufficiently plausible, we cannot take the object out of Shimon's possession.
The three required conditions:
Proof of original ownership: Witnesses are required to confirm that the coat, or any other object, previously belonged to Reuven. Without this, the discussion does not even begin. Equivalent proof is also sufficient, such as Reuven's name and details written inside the coat, which confirms his original ownership with certainty.
A prior rumor: Reuven already circulated a report that his belongings were stolen, prior to the confrontation with Shimon, such as having filed a police report or publicized the theft. Without this condition, we must suspect that he perhaps sold the object himself, and is now regretting it.
He does not usually sell his belongings: Reuven must be the type of person who does not normally sell his property. However, if he is pressed for money and is accustomed to pawning his assets and selling his belongings, we will say that while the object was indeed his, it stands to reason that he sold it.
When all three conditions are met simultaneously, there is a basis to believe that the object in Shimon's possession belongs to Reuven and was stolen from him. Even if Shimon himself is not the thief, Reuven gets his item back.
The words of the mishnah:
"Hamakir keilav usefarav beyad acher" - One who recognizes his belongings in the possession of another: "keilav", his clothes and belongings, or "sefarav", his Torah scrolls. The mishnah uses two examples, as a Torah scroll is not an object that is usually sold, to teach us that the law is the same in both cases.
"Veyatza lo shem geneivah ba'ir" - Even before Reuven saw his coat on Shimon, a rumor had already circulated in the city that the object was stolen, whether through a police report or publicization, until the matter was known to all. When combined with the other conditions detailed by the Gemara, namely proof that the object was originally his and that he is not the type of person who sells his belongings, Shimon is compelled to return the coat to Reuven.
"Yishava lo halokei'ach kamah nasan" - Shimon is entitled to a reimbursement of his expenses. He takes a formal oath while holding a sacred object, and declares to Reuven how much he paid for the item, and Reuven pays him back the amount and takes his coat back.
Why is payment required? Takkanas hashuk:
Strictly speaking, when there is no yei'ush and Reuven has proof of his ownership, there would be grounds for him to take the item from Shimon without paying anything at all, and say to him: You bought a stolen item, and that is not my problem; return what is mine, and go collect from the seller. But the Sages did not want this, because of takanas hashuk, an enactment designed to ensure the stability of commerce. If it were possible to snatch items from buyers without a financial refund, they would avoid buying in the first place. For this very reason, e-commerce sites offer guarantees to their buyers, refunding the money when a flaw in the transaction is discovered. Similarly, the Sages ruled: In this exceptional case, Reuven is allowed to claim back his precious item, but he must refund Shimon the amount he paid, as he swore.
"Ve'im lav" - And if not:
If we do not have all three conditions - the Mishnah does not list them all explicitly, but this is its intention: there is no solid proof of Reuven's original ownership, or word did not spread in the city beforehand that his items were stolen, or Reuven is among those people who sell their belongings to obtain money - then "lo kol heimenno" - the matter does not depend on Reuven's claim alone. We do not accept one side of the story, since Shimon is also standing here, and he too is a potential victim.
"She'ani omer macharan le'acher velakchan zeh heimenno" - for I say he sold them to another, and this one bought them from him. The judge says: I do not know what happened. It is possible that the cloak did indeed belong to Reuven, but he sold it to another person, and that other person sold it to Shimon. Why, then, should Shimon lose out? Perhaps now, since Reuven has become wealthy, he regrets parting with his cloak and wishes to get it back, or he lacks a Torah scroll and wants to take back what was previously his. His mere desire for the item does not grant him the right to receive it.
In summary: Unless all three conditions are met simultaneously, we do not allow Reuven to extract his items from the possessor. And even when he wins the right to get them back, he must compensate Shimon for his expenses according to his oath, by virtue of the rabbinic enactment known as takanas hashuk, which was designed to maintain the stability of commerce.