Jeremiah 34:9-11 NIV

9 Everyone was to free his Hebrew slaves, both male and female; no one was to hold a fellow Jew in bondage.1

References for Jeremiah 34:9

10 So all the officials and people who entered into this covenant agreed that they would free their male and female slaves and no longer hold them in bondage. They agreed, and set them free.
11 But afterward they changed their minds2 and took back the slaves they had freed and enslaved them again.

References for Jeremiah 34:11