פירוש על עבודה זרה 124:8

During the Sabbatical year the people of the house of R. Yannai would borrow produce from poor people (who can collect freely from the fields) before such produce needed to be removed from one’s home. They would pay the poor people back after the Sabbatical year, when produce can be sold. The question is—does this count as engaging in trade with Sabbatical year produce. R. Yohanan says it does not since by the time they compensated them, the original produce no longer existed. This seems to be a sort of legal fiction to circumvent the laws of the Sabbatical year, and also to benefit the poor.