Lev 25:45-46 Moreover of the children of the strangers that do sojourn among you, of them shall ye buy, and of their families that are with you, which they begot in your land: and they shall be your possession.
And ye shall take them as an inheritance for your children after you, to inherit them for a possession; they shall be your bondmen forever: but over your brethren the children of Israel, ye shall not rule one over another with rigor.

Slavery is ok, providing it's only foreigners.