The Babylonian Talmud in Tractate Bava Kama 79 states that “just as the land is bought with money a bill and in possession, so the rent is bought with money, a bill and in possession.” Accordingly, Maimonides in ‘Mishneh Torah’ Laws of Sales 1:18 states: “The rent of the land was purchased with money alone or with a bill alone or by possession.”
But civil law has not determined so, and therefore the land is purchased in a written contract, and the ‘written requirement’ is substantial; rent, according to section 25b of the Lease Law, although there is a preference for a written contract an oral contract is also valid.