What is the ruling on a tenant leasing the rented property to another person without the owner's knowledge? And upon whom does the sin fall if this scenario is impermissible?

There is no objection to subletting the rented property without the original owner's knowledge, unless the lease agreement prohibits it, provided that the new tenant's use of the property is similar to or less damaging than the original tenant's use. The tenant may rent the property to someone who takes their place for the same rent or more. This is the view of Ahmad and Al-Shafi'i.