Leviticus 25:42-46

For they are my servants, whom I brought out of the land of Egypt; they shall not be sold as slaves. You shall not rule over him ruthlessly but shall fear your God. 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.