Leviticus 25:51-55

If there are still many years remaining, he shall refund part of his purchase price in proportion to them for his own redemption;

but if few years remain until the year of jubilee, he shall so calculate with him. In proportion to his years he is to refund the amount for his redemption.

He shall be with him like a worker hired year by year; he shall not rule over him with severity in your sight.

Even if he is not redeemed by these means, he shall still leave in the year of jubilee, he and his sons with him.

For the sons of Israel are My servants; they are My servants whom I brought out from the land of Egypt. I am the Lord your God.