Stirling: "Peragrine, I know it's you. You can stop the voice."
Peragrine: "I know not of this Peragrine you speak of, but he sounds like a really awesome dude with lots of friends. Like seriously.
Stirling: "Oh my god it is him."
(Peragrine probably tried to disguise his voice and trick Stirling at one point, let's be honest here.)
Source: Reviving Bionicle.