Reference for Bava Batra 339:7

והא אמר רבי אבא מודה היה רבי אלעזר במזוייף מתוכו שהוא פסול

[the letter of divorce] are the main factor in the legal separation.<span class="x" onmousemove="('comment',' Git. 21b. Cf. note 5. As in the case of a letter of divorce the validity of the document is entirely dependent on the witnesses whose signatures are appended to it so in the case of a deed of purchase or sale, unless the witnesses who signed it are eligible, the document is invalid. Hence R. Simeon b. Gamaliel maintains that, where one of the witnesses was found to be disqualified for any reason whatsoever, the entire deed is invalid, and right of ownership must be determined by the result of the evidence of witnesses on the statutory period of undisturbed possession of the land, on the part of the present holder. ');">¹²</span> But, surely. R. Abba had said: R. Eleazar agrees that [a deed] is invalid if the irregularity is internal!<span class="x" onmousemove="('comment',' Git. 10b. Though a letter of divorce on which no signatures at all appear is valid (the witnesses to the delivery effecting the legal and final separations), where disqualified witnesses are signed on it, thereby causing an irregularity in the document itself, the deed is invalid. Similarly, in the case of the deed of purchase under discussion, how could R. Simeon b. Gamaliel regard it as valid when, owing to the disqualification of one of the witnesses, an internal irregularity arises in the deed itself! ');">¹³</span>

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