Leviticus 25:40-43

25:40 He must be with you as a hired worker, as a resident foreigner; he must serve with you until the year of jubilee, 25:41 but then he may go free, he and his children with him, and may return to his family and to the property of his ancestors. 25:42 Since they are my servants whom I brought out from the land of Egypt, they must not be sold in a slave sale. 25:43 You must not rule over him harshly, but you must fear your God.