Leviticus 25:53-55

They are to be treated as workers hired from year to year; you must see to it that those to whom they owe service do not rule over them ruthlessly. ‘ “Even if someone is not redeemed in any of these ways, they and their children are to be released in the Year of Jubilee, for the Israelites belong to me as servants. They are my servants, whom I brought out of Egypt. I am the LORD your God.