Leviticus 25:44-46

44“As for your male and female slaves whom you may acquire out of the nations that are around you—from them you may buy male and female slaves.

45You may also acquire from among the children of the foreigners dwelling among you, as well as from their families who are with you—those born in your land—they may also become your property.

46You may also leave them an inheritance for your children after you, to receive as a possession. These may become your slaves permanently. But over your brothers, Bnei-Yisrael, you must not rule over one another with harshness.