Bava Metzia 22A

וכן ירדן שנטל מזה ונתן לזה, מה שנטל ⁠– נטל, ומה שנתן ⁠– נתן.

and likewise, in the case of the Jordan River or another river that took an item from this person and gave it to that person, in all those cases, that which the person took, he took, and that which the person gave, he gave. Likewise, that which the river took, it took, and that which the river gave, it gave. The person who received the item need not return it.

בשלמא גזלן וירדן, דקא חזי להו ומיאש. אלא גנב, מי קא חזי ליה דמיאש? תרגמה רב פפא בלסטים מזוין. אי הכי היינו גזלן! תרי גווני גזלן.

The Talmud asks: Granted in the cases of the robber and the Jordan River, one could say that the owner sees them take the item and despairs of its recovery; but in the case of the thief, who takes the item surreptitiously, does the owner see him take the item and would that lead him to despair? The Talmud explains: Rav Pappa interpreted the term thief in the baraita to be referring to armed bandits [listim]; therefore, the owner is aware that the item was taken and he despairs of its recovery. The Talmud asks: If so, this is the same as a robber, why mention two identical cases? The Talmud answers: The baraita mentioned two types of robbers; in both cases the owner was aware that his item was taken.

תא שמע: שטף נהר קוריו, עציו, ואבניו, ונתנו בתוך שדה חבירו ⁠– הרי אלו שלו, מפני שנתיאשו הבעלים. טעמא דנתיאשו הבעלים, הא סתמא ⁠– לא! הכא במאי עסקינן? כשיכול להציל.

The Talmud suggests: Come and hear a proof from a baraita: If a river swept away one’s beams, one’s wood, or one’s stones and placed them into the field of another, these items belong to the owner of the field due to the fact that the respective owners despaired of their recovery. The Talmud infers from the baraita: The reason they belong to the finder is that the owners despaired; but in an unspecified case, where it is not definitively known that the owners despaired, they do not belong to the finder. Apparently, despair that is not conscious is not considered despair. The Talmud rejects the proof: With what are we dealing here? It is a case where the owners are capable of rescuing the beams, wood, or stones; therefore, their decision not to rescue them is a clear indication of despair.