Parashas Behar · Aliyah 7 · Passuk 25:48
Chabad.org — English translation + Rashi
Torah Temimah cites Sifra / Kiddushin 21a.
English: “There shall be redemption for him.” This teaches that he has a right of redemption.
Classical derasha (Sifra / Bavli Kiddushin).
A Hebrew servant sold to a non-Jew retains the right to be redeemed; the duty falls first upon his relatives.