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.
Nave's Topical Index—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.
Nave's Topical Index—AKJV

Jeremiah 34:14
At the end of seven years let you go every man his brother an Hebrew, which has been sold to you; and when he has served you six years, you shall let him go free from you: but your fathers listened not to me, neither inclined their ear.
Nave's Topical Index—AKJV