Mishnah for Ketubot 9:2

A field from which thorns had been removed may be sown in the eighth year. But if it had been improved upon, or cattle had been allowed to live upon it, it may not be sown in the eighth year. A field which had been improved upon in the seventh year: Bet Shammai says: they may not eat its produce in the seventh year, But Bet Hillel says: they may eat. Bet Shammai says: they may not eat produce of the sabbatical year with an expression of thanks. But Bet Hillel says: they may eat [sabbatical year produce] with an expression for thanks and without an expression of thanks. Rabbi Judah says: the statements must be reversed, for this is one of the instances where Bet Shammai is lenient and Bet Hillel is stringent.