Reference for Bava Batra 345:6

אמר אביי מנא אמינא לה דתניא אחד מן האחין שהשטר חוב יוצא מתחת ידו עליו להביא ראיה מאי לאו הוא הדין לאחריני

holds that proof must be produced,<span class="x" onmousemove="('comment',' Otherwise the debtor can plead that the holder has found the bond in the street or that it was only deposited with him. Hence the statement in the Baraitha that none of the Josephs may present a bond against a third person who could plead that the bond belongs to the other Joseph and that the one who presented it received it only as a deposit or found it. ');">¹⁶</span> for it was stated: 'Letters' are acquired by delivery; Abaye said: He<span class="x" onmousemove="('comment',' The holder of the deed. ');">¹⁷</span> must, however, produce proof;<span class="x" onmousemove="('comment',' Cf. supra note 2. ');">¹⁸</span>

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