Exodus 21:2
If you buy an Hebrew servant, six years he shall serve: and in the seventh he shall go out free for nothing.
Torrey's Topical Textbook—AKJV

Deuteronomy 15:12
And if your brother, an Hebrew man, or an Hebrew woman, be sold to you, and serve you six years; then in the seventh year you shall let him go free from you.
Torrey's Topical Textbook—AKJV