Rashi on Leviticus 25:25/רש"י על ויקרא כ״ה:כ״ה

1כי ימוך אחיך ומכר AND IF THY BROTHER BE WAXEN POOR AND HAS SOLD AWAY [SOME OF HIS POSSESSION] — The introductory words teach us that one is not permitted to sell his real estate except under the pressure of poverty (cf. Sifra, Behar, Chapter 5 1).

2מאחזתו SOME OF HIS POSSESSION — but not the entire property. Scripture thereby teaches you a practical rule that, however needy a man is, he should always leave some immovables (lit., a field) for himself (Sifra, Behar, Chapter 5 1).

3וגאל את ממכר אחיו HE SHALL REDEEM THAT WHICH HIS BROTHER SOLD — and the purchaser has no right to prevent it.