Leviticus 25:40-43

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.