BOOK: "Extreme Programming Explained: Embrace Change, 2nd Edition" (The XP Series) - Kent Beck

The definitive guide to XP is the book by the author (Kent Beck):

https://www.amazon.com/gp/product/0321278658?ie=UTF8

Extreme Programming Explained: Embrace Change, 2nd Edition (The XP Series)

2nd Edition, ISBN-13: 978-0321278654, ISBN-10: 0321278658

PS. Additional info about XP, considered the first of the agile methodologies (long before Scrum):
https://martinfowler.com/bliki/ExtremeProgramming.html