Jeremiah 34:13-14

“This is what the LORD, the God of Israel, says: I made a covenant with your ancestors when I brought them out of Egypt, out of the land of slavery. I said, ‘Every seventh year each of you must free any fellow Hebrews who have sold themselves to you. After they have served you six years, you must let them go free.’ Your ancestors, however, did not listen to me or pay attention to me.