What's the rules with regards to fighting in the NHL?

Question

Sometimes the nearest official will be quick to stop the fight, but at other times they let the fight continue.

What is the actual rule regarding fighting? Or is it down to the officials' discretion?

Answer 1

as soon as one of them slip and hits the ice its over, they have to stay standing.

Answer 2

The answer above is right.

Also as long as both players drop their sticks so it's a fair fight, the ref will allow the fight to continue.