If the owner's claim of a lease is accepted after a period has passed, what is the determined amount of rent?

Primary text

There are two views regarding the amount. The first view mandates the fair market rent ('ujr al-mithl') because if they had agreed on the obligation but differed on the amount, the fair market rent would be due, making it more appropriate here where the obligation itself is disputed. The second view mandates the specified rent ('al-musamma') because the rent was established by the owner's assertion and oath, thus what was sworn to must be fulfilled, like the principle itself.