oldest complete book IN THE WORLD ! (maybe).
it happens to be a hymn book , but its still a book !
Sumerian Temple Hymn, baked clay, circa between 1800 and 1600 BC (Old Babylonian), currently located at the Walters Art Museum.

This tablet, inscribed on all four sides, is one of the best preserved copies of the Sumerian hymn to the temple at Kesh. The popular hymn, written in praise of the temple built for the mother-goddess Nintu in the city of Kesh in southern Mesopotamia, describes the temple in both physical and heavenly terms.