Leviticus 25:44-46 New International Version (NIV)

⁴⁴ “‘Your male and female slaves are to come from the nations around you; from them you may buy slaves. ⁴⁵ You may also buy some of the temporary residents living among you and members of their clans born in your country, and they will become your property. ⁴⁶ You can bequeath them to your children as inherited property and can make them slaves for life, but you must not rule over your fellow Israelites ruthlessly.