I am just wondering about this since I heard that tor exit nodes know the ip of the website the user is visiting
No, a Tor exit node does not know the IP of a .onion site. The only node that knows the real IP of a .onion site is a special node called guard node. It's the first node the hidden service connects to, so it knows the real IP.
You already have an accepted answer, but I'm going to add a clarification anyway.
When connecting with a hidden service (.onion), there is no exit node at all! Exit nodes are gateways to the normal (non Tor) Internet. Hidden services (.onion) don't exit, therefore no exit node.
Guard nodes are entries (although all nodes are bidirectional) to Tor. So yes the guard node knows the real IP of the connecting computer but it knows nothing about .onion hidden services. The guard node cannot identify and locate .onion hidden services.