Leviticus 25:40-43, 45

As a hired servant and a sojourner he shall be with you, and shall serve you until the Year of Jubilee. And then he shall depart from you—he and his children with him—and shall return to his own family. He shall return to the possession of his fathers. For they are My servants, whom I brought out of the land of Egypt; they shall not be sold as slaves. You shall not rule over him with rigor, but you shall fear your God.

Moreover you may buy the children of the strangers who dwell among you, and their families who are with you, which they beget in your land; and they shall become your property.