Mischna zu Schemot 13:12

The peels and the blossom of the pomegranate, the nutshells, and fruit seeds the laws of sabbatical produce apply to them and to their money substitutes. The dyer may use them for himself, but he may not dye with them for a wage, since one may not engage in business with seventh year produce, or with first-born animals, or with terumah, or with nevelah, or with trefah, or with reptiles or with creeping things. One should not buy field-vegetables and sell them in the market. But he may gather them and have his son sell them on his behalf. If he gathered them for his own use, and some remains over, he may sell them.