Reference for Bava Metzia 38:18

אמר רבא

as he [this person]<span class="x" onmousemove="('comment',' V. p. 121, n. 7. ');">¹⁵</span> will be legally entitled to it,<span class="x" onmousemove="('comment',' Because of the son's statement that his father had given it to that person. ');">¹⁶</span> and we shall both share [in the gain].'<span class="x" onmousemove="('comment',' This indicates the motive which would prompt the son to make the false statement — a conspiracy between him and that person to obtain possession of the gift and to divide it. ');">¹⁷</span> We therefore say to him [the son]: We cannot give this document to this person,<span class="x" onmousemove="('comment',' V. p. 121, n. 7. ');">¹⁵</span> as it may be that your father did write it [for him] but did not give it to him, and that you gave it to a different person instead, and have now changed your mind. Now, if you speak the truth [in saying] that your father gave it to him, go now and write him another deed, for then, even if your father did not give it to him, and you wrote it for a different person, that other person will suffer no loss, for if the first document and the last are produced, the first is valid.<span class="x" onmousemove="('comment',' As when the two documents have been written by the son, who is a healthy person, the owner of the first document will be entitled to the gift, and the writing of the second document will make no difference. ');">¹⁸</span> Our Rabbis taught: If one finds a receipt<span class="x" onmousemove="('comment',' In which a wife acknowledged having received payment of her Kethubah while she was still living with her husband. ');">¹⁹</span> [the law is that] when the wife admits [its genuineness] one shall return it to the husband, [and that] when the wife does not admit [its genuineness] one shall not return it to either party. It is thus taught that when the wife admits, [the document] shall be returned to the husband: Ought we not to apprehend that she may have written it with the intention of giving it [to the husband] in Nisan, and that [in reality] she did not give it [to him] until Tishri,<span class="x" onmousemove="('comment',' When she received payment. ');">²⁰</span> and that in the interval between Nisan and Tishri she went and sold [the value of] her <i>Kethubah</i> for a consideration,<span class="x" onmousemove="('comment',' Lit., 'for the benefit of a pleasure'; for a trifle, as in view of the possibility of the wife's death preceding that of her husband the buyer of the Kethubah stands to lose the price he pays, and this reduces the value of the Kethubah if sold before it becomes due. ');">²¹</span> while the husband may produce the receipt, [showing] that it was written in Nisan,<span class="x" onmousemove="('comment',' So that the date of the receipt produced by the husband will be taken as proof that it preceded the sale of the Kethubah by the wife, and the buyer will lose his claim. ');">²²</span> and he will thus be able to deprive unlawfully those who bought [the value of the <i>Kethubah</i> of what is due to them]? — Raba answered:

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