Leviticus 25:44-46

44Your male and female slaves are to be from the nations around you; you may purchase male and female slaves.

45You may also purchase them from the aliens residing with you, or from their families living among you — those 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 concerning your brothers, the Israelites, you must not rule over one another harshly.