Commenting on Numbers 25:36-27, Gordon Wenham notes “Interest-free loans are well attested in ancient financial records, and laws against taking excessive interest are also known, but Israel is alone in totally prohibiting interest payments on loans to the poor. These loans were essentially charitable: they enabled a poor farmer to buy enough seed corn for the next season.”

Well, not exactly free (which is notoriously not helpful for the poor), but loans without interest between Israelites was mandated by law.