Midrash su Levitico 25:12

3) (Vayikra 25:12) ("For it is Yovel; holy shall it be to you. From the field shall you eat its produce") "For it is Yovel; holy": Just as (the holiness of) what is holy attaches itself to its money (i.e., the money with which it was redeemed), so, (the prohibition of) shevi'ith attaches itself to its money. But (in that case, let us say that) just as with what is holy the money is attached but the object loses its holiness, so, with shevi'ith (i.e., let the fruit itself be permitted)! It is, therefore, written "shall it be" — it (Yovel) retains its sanctity. So that "shevi'ith" attaches to the very last (object) and the (original) fruit is forbidden. How so? If he took meat in exchange for the fruits of shevi'ith, both are removed on shevi'ith. If he exchanged the meat for fish, the meat leaves (the category of "shevi'ith") and the fish enters. (If he exchanged) the fish for oil, the fish leaves and the oil is attached. The very last is attached and the (original) fruit remains forbidden.

4) "From the field shall you eat its produce": So long as you eat it (i.e., so long as it is found) in the field, you may eat it in the house. If it has "ended" from the field, end it (i.e., remove it) from the house. And from what you eat in the field, you may eat in the house.

5) From here they ruled: If one puts three sorts of pressed vegetables into one vessel — R. Eliezer says: If one of them ended from the field, he must remove the entire vessel (from the house). R. Yehoshua says: He keeps on eating until the last (of the three kinds to ripen) ends from the field. R. Gamliel sys: A variety whose kind has ended from the field must be removed from the vessel, and the halachah is in accordance with him. R. Shimon says: Every vegetable is alike vis-à-vis removal (i.e., any kind of vegetable in the house may be eaten so long as any kind of vegetable remains in the field.) Portulacea may be eaten (in the house) until the tares come to an end in the valley of Beth Netopha.