Bava Batra 28B

ואידך, כי לא נגח ⁠– מאי לשלם? הכא, כיון דאכלה תלת שני ⁠– קיימא לה ברשותיה.

and the requirement for there to be another, 4th, incident for the owner to be liable to pay full damages exists because before it gores after having become a forewarned ox, what is there for the owner to pay? Here, once he has worked and profited from the land for 3 years, the land is established as being in his possession.

אלא מעתה, חזקה שאין עמה טענה תיהוי חזקה! אלמה תנן: כל חזקה שאין עמה טענה, אינה חזקה?

The Talmud asks: If that is so, according to the explanation that the forewarned ox is the source for the presumption of ownership with regard to land, even possession that is not accompanied by a claim, i.e., where the possessor has no explanation as to how he acquired it, should be sufficient to establish the presumption of ownership, just as goring 3 times automatically establishes its having the status of a forewarned ox. Why did we learn in a Mishnah (41a): Any possession that is not accompanied by a claim explaining how the possessor became the owner is not sufficient to establish the presumption of ownership?

טעמא מאי ⁠– דאמרינן: דלמא כדקאמר, השתא איהו לא טעין, אנן ליטעון ליה?!

The Talmud answers: What is the reason that possession that is not accompanied by a claim is not sufficient to establish the presumption of ownership? Because in a standard case where one has presumptive ownership, we say that even if the claimant proves that the field was once his, since the other is in possession of the land, perhaps the truth is as he says, that he purchased it from the previous owner. But now that he himself does not claim that he purchased it, will we claim this for him?