Sifrei Mitzvot sobre Êxodo 34:21

That is that He commanded us to rest from any agricultural work on the seventh year. And that is His, may He be exalted, saying, "you must cease plowing and harvesting" (Exodus 34:21). And this command has already been repeated several times: He said, "[But] in the seventh year, the land shall have a sabbath of complete rest (shabbaton)" (Leviticus 25:4) - and we have already seen (Sefer HaMitzvot, Positive Commandments 90) that this, "shabbaton," is a positive commandment. And He also said, "and the land shall rest" (Leviticus 25:2). And the regulations of this commandment are also already explained in Tractate Sheviit. But its obligation by Torah law is only in the Land of Israel. (See Ki Tissa; Mishneh Torah, Sabbatical Year and the Jubilee 1.)