When we need a hidden service descriptor, we have to build a circuit to access a hidden service directory. Is this circuit a normal circuit, or is the third hop of the circuit an exit node?
Every aspect of accessing a hidden service takes place within the Tor network. No exit nodes need to be involved.
The process is well explained here: Tor: Hidden Service Protocol
... the client can initiate connection establishment by downloading the descriptor from the distributed hash table. ... the client now knows the set of introduction points and the right public key to use. Around this time, the client also creates a circuit to another randomly picked relay and asks it to act as rendezvous point by telling it a one-time secret. ... the client sends an introduce message including the address of the rendezvous point and the one-time secret to one of the introduction points ... The service creates a circuit to the rendezvous point and sends the one-time secret to it in a rendezvous message...