Shoutout goes to Your_Queen_Of_Crazy for answering first. The correct answer was: Percy said it in Percy Jackson and the Battle of the Labyrinth.
Mentions go to hockeyandbookfan2021 (for getting the series right!) and 5SecondsOfSwim (for getting the book and the sayer right!). 👏

Kill me. If you've ever been my friend, kill me.