Reference for Gittin 101:12

אלא בתו דבתנאי בית דין קאכלה לא מהני לה קנין בת אשתו דלאו בתנאי בית דין קאכלה מהני לה קנין

also should draw on mortgaged property]? — We presume that the transfer was made on behalf of the one but not of the others. On what ground do you decide thus? — Because the daughter of his wife who was already born at the time of the transfer can benefit from the transfer, but his own daughter who was not yet born at the time of the transfer cannot benefit from it. But are we not to assume that both had already been born at the time of the transfer, [and if you ask how can this be, I answer,] supposing he had divorced her and then taken her back?<span class="x" onmousemove="('comment',' And afterwards made the agreement along with the transfer. Hence the transfer cannot be the reason. ');">¹¹</span>

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