Leviticus 25:44-46

44And as for your male and female slaves whom you may have—from the nations that are around you, from them you may buy male and female slaves.

45Moreover you may buy the children of the strangers who dwell among you, and their families who are with you, which they beget in your land; and they shall become your property.

46And you may take them as an inheritance for your children after you, to inherit them as a possession; they shall be your permanent slaves. But regarding your brethren, the children of Israel, you shall not rule over one another with rigor.