Is it permissible for the landlord to ask the tenant to pay two months' rent in advance in exchange for exempting him from paying the third month's rent, provided that monthly payments resume thereafter?

It is permissible for the owner to expedite the tenant's installments and waive one installment in return for that, and this is known as the issue of "give discount for early payment." It is permissible and not considered usury (riba). Abdullah ibn Abbas and Ibn Taymiyyah held this view, and it was adopted by the Islamic Fiqh Council and the Permanent Committee.