Leviticus 25:43

40 As a hired servant, and as a temporary resident, he shall be with you; he shall serve with you until the Year of Jubilee.

41 Then he shall go out from you, he and his children with him, and shall return to his own family, and to the possession of his fathers.

42 For they are my servants, whom I brought out of the land of Egypt. They shall not be sold as slaves.

43 You shall not rule over him with harshness, but shall fear your God.

44 “‘As for your male and your female slaves, whom you may have from the nations that are around you, from them you may buy male and female slaves.

45 Moreover, of the children of the aliens who live among you, of them you may buy, and of their families who are with you, which they have conceived in your land; and they will be your property.

46 You may make them an inheritance for your children after you, to hold for a possession. Of them you may take your slaves forever, but over your brothers the children of Israel you shall not rule, one over another, with harshness.