What is the ruling on hiring a man with an open-ended contract?

The lease is a contract for usufructs, and for its validity, jurists stipulate that the usufruct must be known, and this is by knowing the duration for which the lease ends, such that it is known, like a month or a year. There is no limit to the maximum duration of a lease. Any lease contract that lacks a statement of the duration must be revoked due to the uncertainty (gharar (definition)) and ignorance (jahalah) within it. It is not permissible to combine the specification of a duration and a task, according to the majority of scholars.