Reference for Bava Metzia 32:2

אמר רב הונא אמר רב האומר לחברו שדה שאני לוקח לכשאקחנה קנויה לך מעכשיו קנה

R. Huna said in the name of Rab: If one says to his neighbour: 'The field which I am about to buy shall, when I have bought it, be sold to you from now,' [the neighbour] acquires it.<span class="x" onmousemove="('comment',' The moment the seller has bought the field from the original owner it becomes the property of the buyer, and the seller ends the transaction. ');">²</span>

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