Reference for Bava Metzia 148:7

אמר ליה אימור דאמר רבי שמעון בחד תרעא בתרי תרעי מי אמר דאי לא תימא הכי מי שפרע בלוקח לרבי שמעון לית ליה

so that, if he stipulated for the lowest price, he receives it at current values, but if not, he must accept it at previous prices, because his money has effected possession for him; whereas in the opinion of the Rabbis, whether he stipulated or not, he can take it at present prices, for a man's intention is for the lowest price?<span class="x" onmousemove="('comment',' Since the Rabbis maintain that the vendee may rescind the sale even without a drop in price, but that he is subject to the curse, it may be that if the price falls, he is even morally entitled to retract, for a 'most favoured-sale' is implicit in every such transaction. ');">⁷</span>

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