When in the book does it state Annabeth's and Grover's friendship with Percy and what page?

"All the way into the city, I put up with Nancy Bobofit, the freckly, redheaded kleptomaniac girl, hitting my best friend Grover in the back of the head with chunks of peanut butter-and-ketchup sandwich." pg.4

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"A voice that was definitely Grover's said "... worried about Percy, sir." I froze.
I'm not usually an eavesdropper, but I dare you to try not listening if you hear your best friend talking about you to an adult." pg. 21

I see no reference to Percy describing Annabeth as his best friend.