Leviticus 25:27, 51-52

then let him count the years of the sale thereof, and restore the overplus unto the man to whom he sold it; that he may return unto his possession.

If there be yet many years behind, according unto them he shall give again the price of his redemption out of the money that he was bought for. And if there remain but few years unto the year of jubile, then he shall count with him, and according unto his years shall he give him again the price of his redemption.