Leviticus 25:44-46

44Both thy male and female slaves, which thou shalt have, shall be from the heathen that are around you; from them shall ye buy male and female slaves. 45Moreover of the children of the strangers that sojourn among you, of them shall ye buy, and of their families that are with you, whom they begat in your land: and they shall be your possession. 46And ye shall take them as an inheritance for your children after you, to inherit them for a possession; they shall be your slaves for ever: but over your brethren the children of Israel, ye shall not rule one over another with rigour.1