Leviticus 25:44-46

44Your menservants and maidservants shall come from the nations around you, from whom you may purchase them. 45You may also purchase them from the foreigners residing among you or their clans living among you who are born in your land. These may become your property. 46You may leave them to your sons after you to inherit as property; you can make them slaves for life. But as for your brothers, the Israelites, no man may rule harshly over his brother.