Leviticus 25:43

40 But let him be with you as a servant working for payment, till the year of Jubilee;

41 Then he will go out from you, he and his children with him, and go back to his family and to the property of his fathers.

42 For they are my servants whom I took out from the land of Egypt; they may not become the property of another.

43 Do not be a hard master to him, but have the fear of God before you.

44 But you may get servants as property from among the nations round about; from them you may take men-servants and women-servants.

45 And in addition, you may get, for money, servants from among the children of other nations who are living with you, and from their families which have come to birth in your land; and these will be your property.

46 And they will be your children's heritage after you, to keep as their property; they will be your servants for ever; but you may not be hard masters to your countrymen, the children of Israel.