Deuteronomy 15:18

He hath been worth a double-hired servant to thee; or, he deserves double wages to an hired servant, because he served thee upon better terms, both without wages, which hired servants require, and for a longer time, even for six years, as it here follows, whereas servants were ordinarily hired but from year to year, Leviticus 25:53, or at most but for three years, as they gather from this place and Isaiah 16:14.