Jeremiah 34:13-14

13Thus saith Jehovah the 1God 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, a Hebrew, who hath sold himself unto thee; 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.