Parashas Behar · Aliyah 6 · Passuk 25:39
Chabad.org — English translation + Rashi
Torah Temimah cites Sifra / Kiddushin 15a–22a.
English: “And if your brother becomes poor with you and is sold to you.” This teaches that a person may not sell himself unless he has become impoverished.
Classical derasha (Sifra / Bavli Kiddushin).
Self-sale into servitude is permitted only under genuine poverty; one may not sell oneself merely for profit or convenience.