Leviticus 25:40-43

As a hired servant, and as a sojourner, he shall be with thee; he shall serve with thee unto the year of jubilee: then shall he go out from thee, he and his children with him, and shall return unto his own family, and unto the possession of his fathers shall he return. For they are my servants, whom I brought forth out of the land of Egypt: they shall not be sold as bondmen. Thou shalt not rule over him with rigor, but shalt fear thy God.