The Source of Magic

From Author Wars - https://authorwars.com/publications/the-source-of-magic-203129.html

Overview:

Title: The Source of Magic
Author: Piers Anthony
Year: 1979
ISBN-10: 0345272846
Publisher: Del Rey / Ballantine
Price: $1.95
Pages: 326
Binding: Paperback
Type: Novel
Title Reference: The Source of Magic
Notes: Stated 3rd printing.
Copyright page gives ISBN as 0-345-28765-7 which wasn't used until the 4th printing.