The Holy Bible...I think.
Actually, The Bible was not the first book. Books have been in existence for thousands of years. Also, how you define "the Bible" depends changes the equation.
The King James Version, which one version many people consider to be the actual Bible (matter of opinion) wasn't in existence until the early 1600s, when is was transcribed by King James scribes.
The Gutenberg Bible, which was the first Bible to be printed on a printing press, was printed in the 1450s.
Other versions existed before that, but they are all translations of the orginal letter and manuscripts from the writers, and for that matter, there were many letters and manuscripts written by some of the same people that were not included in many of the versions of the Bible that are in existence.
Best Word Book Ever was created in 1963.
Why I Will Never Ever Ever Ever Have Enough Time to Read This Book was created in 2000.
First Book was created in 1992.
The Conchologist's First Book was created in 1839.
The first book Kathryn Lasky ever wrote was "I Have Four Names for My Grandfather." It was published in 1979.
Guardian First Book Award was created in 1965.
Dr.Suess's first book he ever wrote was And to Think That I Saw it on Mulberry Street.
The First Time Ever I Saw Your Face was created on 1972-03-07.
First Light - Wellum book - was created in 2002-01.
The first ever sphinx created was in Giza.
The first book Stephanie Meyer ever wrote was Twilight
First Tuesday Book Club was created on 2006-08-01.