Reference for Bava Batra 307:7

ואי איתמר בהא בהא קאמר ר' מאיר אבל בהך אימא מודה להו לרבנן צריכא

[it might have been assumed that] in that [case only] did the Rabbis say [that attestation of the witnesses was necessary] because the witnesses are all-powerful and they themselves impair [the validity of] the document,<span class="x" onmousemove="('comment',' Hence the debtor's admission is disregarded. ');">²⁵</span> but here,<span class="x" onmousemove="('comment',' Our Mishnah. ');">²⁶</span> where all [the force of the document] does not depend on him,<span class="x" onmousemove="('comment',' The donor. ');">²⁷</span> it might have been assumed [that he is] not [believed].<span class="x" onmousemove="('comment',' When, after admitting that he wrote the deed, he states that he was a sick man when he made the gift. ');">²⁸</span>

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