Leviticus 25:34 "But the field of the pasture land of their cities may not be sold"

The Levites, who serve in the Beit Hamikdash, are granted their own cities in which to live. This is their portion of Eretz Yisrael. In addition to the city, they are given land near their cities for their animals.

The Torah designated these areas for the Levites and they may not be sold or used for any other purpose.