Deuteronomy 15:12
"And if thy brother, an Hebrew man, or an Hebrew woman, be sold unto thee, and serve thee six years; then in the seventh year thou shalt let him go free from thee."
Cross References (ranked by relevance)
Jeremiah 34:14
At the end of seven years let ye go every man his brother an Hebrew, which hath been sold unto thee; and when he hath served thee six years, thou shalt let him go free from thee: but your fathers hearkened not unto me, neither inclined their ear.
Deuteronomy 15:1
At the end of every seven years thou shalt make a release.