Parashas Behar · Aliyah 7 · Passuk 25:49
Chabad.org — English translation + Rashi
Torah Temimah cites Sifra / Kiddushin 21a.
English: “Or his uncle or his uncle’s son shall redeem him.” From here [we learn] that the closer relatives take precedence.
Classical derasha (Sifra / Bavli Kiddushin).
The order of redeemers follows proximity of kinship; if no relative redeems, the servant may redeem himself when his means improve.