As found in the Old Librarian's Almanack, 1773, which says:

"And what Condemnation shall befit the accurst Wretch (for he cannot justly claim the title of Man) who pilfers and purloins for his own selfish ends such a precious article as a Book? I am minded of the Warning display'd in a Library of the Popish Monastery of San Pedro at Barcelona. This is the version English'd by Sir Matthew Mahan, who saw it writ in Latin in the Monastery, as he himself describes in his learn'd Book, 'Travels in Spanish Countries, 1712'"

For him that stealeth a Book from this Library, let it change to a serpent in his hand and rend him.
Let him be struck with Palsy, and all his Members blasted.
Let him languish in Pain, crying aloud for Mercy and let there be no surcease to his Agony till he sink to Dissolution.
Let Book-worms gnaw his Entrails in token of the Worm that dieth not, and when at last he goeth to his final Punishment let the Flames of Hell consume him for ever and aye.