Reference for Bava Batra 314:7

הא מני ר' מאיר היא דאמר אדם מקנה דבר שלא בא לעולם

[Is this land] mortgaged to the first [lender],<span class="x" onmousemove="('comment',' Since his security was obtained before the second loan was incurred, he is also entitled to the priority of his claim. ');">²²</span> or is it mortgaged to the second?<span class="x" onmousemove="('comment',' Lit., 'last'. As it might be maintained that the hold of the first creditor on the property which was non-existent at the time of the loan is not sufficiently strong to prevent the debtor from withdrawing it from him and assigning it as security to a second creditor. ');">²³</span> — R. Nahman replied: We [also] have raised the same<span class="x" onmousemove="('comment',' Lit., 'that'. ');">²⁴</span> question,<span class="x" onmousemove="('comment',' Lit., 'thing'. ');">²⁵</span>

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