Leviticus 25:44-46

44As for your male and female slaves whom you may have—you may acquire male and female slaves from the pagan nations that are around you.

45Moreover, from the children of the strangers who live as aliens among you, from them you may buy slaves and from their families who are with you, whom they have produced in your land; they may become your possession.

46You may even bequeath them as an inheritance to your children after you, to receive as a possession; you can use them as permanent slaves. But in respect to your fellow countrymen, the children of Israel, you shall not rule over one another with harshness (severity, oppression).