Reference for Bava Batra 56:5

התם (שמות כא, כט) והועד בבעליו כתיב הכא חברך חברא אית ליה וחברא דחברך חברא אית ליה

that possession without a plea of justification does not confer a legal title? — The reason why [we confirm the holder in possession when he pleads justification] is because it is possible that his plea is truthful.<span class="x" onmousemove="('comment',' Lit., 'as he says now', E.g., if the claimant says, 'You stole it from me,' and the holder says, 'I bought it from you,' the fact that he has had the use of the land for three years creates a presumption that he is speaking the truth. ');">⁴</span>

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