Jeremiah 34:8-10

This is the word that came to Jeremiah from the LORD, after King Zedekiah had made a covenant with all the people who were at Jerusalem to proclaim liberty to them: that every man should set free his male and female slave—a Hebrew man or woman—that no one should keep a Jewish brother in bondage. Now when all the princes and all the people, who had entered into the covenant, heard that everyone should set free his male and female slaves, that no one should keep them in bondage anymore, they obeyed and let them go.