Leviticus 25:42-46

For they are my servants, whom I brought forth out of the land of Egypt: they shall not be sold as bondmen. Thou shalt not rule over him with rigor, but shalt fear thy God. And as for thy bondmen, and thy bondmaids, whom thou shalt have; of the nations that are round about you, of them shall ye buy bondmen and bondmaids. Moreover of the children of the strangers that sojourn among you, of them shall ye buy, and of their families that are with you, which they have begotten in your land: and they shall be your possession. And ye shall make them an inheritance for your children after you, to hold for a possession; of them shall ye take your bondmen for ever: but over your brethren the children of Israel ye shall not rule, one over another, with rigor.