Jeremiah 34:13-14

13Thus saith the LORD, the God of Israel: I made a covenant with your fathers in the day that I brought them forth out of the land of Egypt, out of the house of bondage, saying,

14At the end of seven years ye shall let go every man his brother that is an Hebrew, which hath been sold unto thee, and hath served thee six years, thou shalt let him go free from thee: but your fathers hearkened not unto me, neither inclined their ear.