Reference for Bava Metzia 126:4
אמר ליה אביי לרב יוסף אלא מעתה מותר ללות סאה בסאה משום דמצי א"ל שקילא טיבותיך ושדייא אחיזרי דאמר ליה חטי דקדחי באכלבאי א"ל התם הלואה הכא זביני
Rabbah and R. Joseph both said: Why did the Rabbis rule, A man may contract to supply [provisions] at the current market price, even if he has none? Because he [the purchaser] can say to him [the vendor], 'Take your favours and throw them in the bush! How do you benefit me? Had I money, I could have bought cheaply in Hini and Shili.'<span class="x" onmousemove="('comment',' [On Hini and Shili, v. B.B. (Sonc. ed.) p. 753, n. 6. There was the central corn market, which supplied corn throughout Northern Babylon, and where wheat was procurable at lower prices (v. Obermeyer, op. cit. p. 32). I.e., 'I could buy it there before the rise in prices,' and thus the purchaser derives no benefit by advancing the money to the seller. The question of usury consequently does not arise.] ');"><sup>3</sup></span>