Is it valid to establish a *Musāqāh* contract on one of two unspecified orchards?

Primary text

It is invalid to establish the *Musāqāh* contract upon one of two specific orchards without clear designation. This is because the contract involves an exchange (*mu'āwaḍah*) where the intent (*gharaḍ*) varies based on the specific subject matter, thus it cannot be validly contracted upon an unspecified item, similar to a sale.