Midrash su Levitico 25:30

3) I might think that since they were given the advantages of both houses, (which are released immediately on Yovel) and of fields, (which are released by deduction of money) then (in certain instances) they are not released on Yovel; it is, therefore, written "and on the Yovel it shall go out."

4) (Vayikra 25:32) ("And the cities of the Levites, the houses of the cities of their holding, a perpetual redemption shall there be for the Levites.") "And the cities of the Levites, the houses of the cities of their holding": What is the intent of this? Because it is written "a perpetual redemption shall there be for the Levites," I might think (that the same applies to) bondsmen, writs, and movables; it is, therefore, written "And the cities of the Levites, the houses of the cities of their holding." "a perpetual redemption shall there be for the Levites": What is the intent of this? Because it is written (Vayikra 25:15) (a minimum of two) "years shall you buy from your fellow," I might think (that this restriction applies) even to the Levites; it is, therefore, written "a perpetual redemption shall there be for the Levites" (i.e., they may redeem it even immediately after the sale).

5) (another answer:) Because it is written (Vayikra 25:30) "And if it (the house) is not redeemed until its fulfillment of a complete year, etc.", I might think (that this restriction applies) even to the Levites, it is, therefore, written "a perpetual redemption shall there be for the Levites." (another answer):) Because it is written (Vayikra 27:20-21) "And if he does not redeem the field, and if he sells the field to another man, it shall not be redeemed again. And the field shall be, when it goes out on the Yovel, holy to the L–rd, as a devoted field; to the Cohanim shall be his holding" — I might think that the same applies to the Levites; it is, therefore, written "a perpetual redemption shall there be for the Levites."