Deuteronomy 15:18

You should not consider it difficult to let him go free, for he will have served you for six years, twice ¹  the time of a hired worker; the Lord your God will bless you in everything you do.

De 15:10; Isa 16:14; Isa 21:16; Lu 17:7,8

¹ tn The Hebrew term מִשְׁנֶה (mishneh, “twice”) could mean “equivalent to” (cf. NRSV) or, more likely, “double” (cf. NAB, NIV, NLT). The idea is that a hired worker would put in only so many hours per day whereas a bondslave was available around the clock.