Reference for Bava Batra 308:7

לימא ר' מאיר היא דאמר מודה בשטר שכתבו אינו צריך לקיימו ולא רבנן

[for something] which I sold you but [for which] you did not pay me the price", then if witnesses<span class="x" onmousemove="('comment',' To testify that his statement, which invalidates the deed, is in accordance with the facts, ');">²³</span> are available, one must be guided by<span class="x" onmousemove="('comment',' Lit., 'go after'. ');">²⁴</span> witnesses, but if [they are] not [available] one is to be guided by<span class="x" onmousemove="('comment',' To testify that his statement, which invalidates the deed, is in accordance with the facts, ');">²³</span> the deed.'<span class="x" onmousemove="('comment',' I.e., since the seller once admitted that the deed was written by him, his attempt to disqualify it is disregarded. ');">²⁵</span>

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