Reference for Leviticus 25:34

וּֽשְׂדֵ֛ה מִגְרַ֥שׁ עָרֵיהֶ֖ם לֹ֣א יִמָּכֵ֑ר כִּֽי־אֲחֻזַּ֥ת עוֹלָ֛ם ה֖וּא לָהֶֽם׃ (ס)

But the fields of the open land about their cities may not be sold; for that is their perpetual possession.