House of Books
After Link completes the Eastern Palace, Sahasrahla will give Link the Pegasus Boots and tells him to find the other two Pendants of Virtue. His quest takes him to the Desert of Mystery, the location of the Desert Palace. However, the entrance is blocked off.
The Book of Mudora is found on top of one of the book shelves within the House of Books. Link cannot ordinary reach this book, however, he can dash with his Pegasus books into the shelf, causing the book to fall to the ground. The Book of Mudora can be used to read Hylian, which will grant Link access to the Desert Palace. Additionally the book will allow Link to read the two Tablets found in the Overworld, allowing Link to acquire the Bombos Medallion and Ether Medallion.
Link acquires the Book of Mudora within the House of Books