The Book of Truth is the foundational text of the Gzilt civilization's religion.
Claimed to have been found on a set of of inscribed slates inside a meteorite by Briper Drodj. Added to by Drodj as and when he was inspired by dreams that seemed to follow on.
The slates either vanished or were destroyed in a temple fire set by unbelievers.
Drodj and his generals conquered their entire world.
Briper Drodj himself vanished somewhat mysteriously, just as he was, allegedly, about to add to the book.
What sets the Book of Truth apart from (all?) other holy books is that it was neither vague or inaccurate. For two thousand years it was unambiguosly correct when predicting technological advances.