Leviticus 25:44-46

As for your male and female slaves whom you may have: you may buy male and female slaves from among the nations that are around you. You may also buy from among the strangers who sojourn with you and their clans that are with you, who have been born in your land, and they may be your property. You may bequeath them to your sons after you to inherit as a possession forever. You may make slaves of them, but over your brothers the people of Israel you shall not rule, one over another ruthlessly.