מדרש על דברים 15:18

6) — whence we derive that one who was sold to a gentile has the upper hand (in the reckoning). Whence is it derived that when he is sold to a Jew, when he is redeemed he has the upper hand? From "hired man" (here) - "hired man" (Devarim 15:18, with respect to one who is sold by beth-din) — a gezeirah shavah (identity) — Just as with "hired man" mentioned in respect to (his being sold to) a gentile, he (the servant) has the upper hand (in his redemption), so, with "hired man" mentioned in respect to (his being sold to) a Jew, he (the servant) has the upper hand in his redemption.