Reference for Bava Metzia 28:2

ואיכא דאמרי אפילו באחריות נמי דאמר ליה אחוי טרפך ואשלם לך

but if he has taken possession of it he cannot retract,<span class="x" onmousemove="('comment',' Even if he has not paid yet, for the buyer acquires the land legally when he takes possession of it, and the purchase price, if not paid, becomes a debt due to the seller (Rashi). ');">²</span>

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