Parashas Behar · Aliyah 5 · Passuk 25:34
Chabad.org — English translation + Rashi
Torah Temimah cites Sifra / Arakhin 33b.
English: “And the open land of their cities shall not be sold.” This teaches that one may not sell the migrash (open land surrounding the city).
Classical derasha (Sifra / Bavli Arakhin).
The open pasture-land (migrash) surrounding Levitical cities may never be sold; it is an everlasting holding.