Reference for Bava Metzia 126:5
אמר ליה אדא בר אבא לרבא והא בעי למיתב זוזי לספסירא א"ל דקא יהיב ליה נמי רב אשי אמר זוזי דאינשי אינהו עבדי ליה ספסירותיה:
Abaye said to R. Joseph: If so, should it not be permitted to lend a <i>se'ah</i> for a <i>se'ah</i>, since he [the borrower] could say, Take your favours and throw them in the bush! For,' he could argue, 'would my wheat have gone to ruin in my granary?' — He replied: There it is a loan, here a purchase. R. Adda b. Abba said to Raba: But he would have to pay money to a broker!<span class="x" onmousemove="('comment',' By paying for the wheat beforehand the buyer saves the broker's fee, which he would have had to pay each time he wanted to make a purchase. This saving constitutes interest on his money. ');"><sup>4</sup></span>