Hiring/Renting: Renting on a Month-by-Month Basis
Practical Laws of Islam as per the teachings of Ayatullah Sistani
Ruling 2201
If a person says to a lessee, ‘I have given the house on rent to you for £1000 a month’, or he says to him, ‘I have given the house on rent to you for one month for £1000; after that, for as long as you reside in the house, the rent will be £1000 a month’, then, as long as the beginning of the rental period is known, the rental agreement is in order for the first month.
-Ayatullah Sistani, Practical Laws of Islam, Hiring/Renting (Ijarah)