Reference for Bava Kamma 205:2
אמר מר הלוקח שדה בשם חבירו אין כופין את המוכר למכור זימנא אחריתי פשיטא מהו דתימא מצי א"ל מידע ידעת דאנא לנפשאי שקילנא ופנחיא בעלמא הוא דקבעינא וזוזי בכדי לא שדינא אלא אדעתא דכתב ליה שטרא אחרינא קא משמע לן דאמר ליה עניינא עבדי לך בהדי ההוא דזבנת ליה בשמיה ויכתוב לך שטרא אחרינא
R. Kahana transmitted some money for the purchase of flax. But as flax subsequently went up in price, the owners of the flax sold it [on his behalf]. He thereupon came before Rab and said to him: What shall I do? May I go and accept the purchase money?<span class="x" onmousemove="('comment',' For which the flax was sold to the subsequent purchasers; would the acceptance of this increase not be a violation of the laws of usury; v. Lev. XXV, 36-37. Cf. also B.M. V, 1. ');"><sup>3</sup></span> — He replied to him: If when they sold it they stated that it was Kahana's flax, you may go and receive the money,<span class="x" onmousemove="('comment',' For in this case they acted on your behalf and the purchase money received was given to become yours. ');"><sup>4</sup></span> but if not you may not accept it.<span class="x" onmousemove="('comment',' For it would appear that for a smaller amount of money received from you, you were subsequently given a bigger sum, and this is against the spirit of the law of usury. ');"><sup>5</sup></span> But was this ruling made in accordance with the view of the Western scholars who asked: 'Who was it that informed the vendor of the wheat so that he might transfer the ownership of his wheat to the owner of the money?<span class="x" onmousemove="('comment',' V. supra p 594. So that in this case too the purchase money received from the subsequent vendees was not automatically transferred to R. Kahana when his name was not mentioned at the time of the sale. ');"><sup>6</sup></span>