Leviticus 25:40-43, 45

He shall be with you as a hired man, as if he were a sojourner; he shall serve with you until the year of jubilee. He shall then go out from you, he and his sons with him, and shall go back to his family, that he may return to the property of his forefathers. For they are My servants whom I brought out from the land of Egypt; they are not to be sold in a slave sale. You shall not rule over him with severity, but are to revere your God.

Then, too, it is out of the sons of the sojourners who live as aliens among you that you may gain acquisition, and out of their families who are with you, whom they will have produced in your land; they also may become your possession.