Muslims accept the original unaltered Torah (as revealed to Moses) and the original unaltered Bible (as revealed to Jesus) since they were revealed by God. But none of these scriptures exist today in their original form or in their entirety. Therefore, Muslims follow the subsequent, final and preserved revelation of God, the Qur'an. 

The Qur'an was not authored by Muhammad. It was authored by God, revealed to Muhammad (through angel Gabriel) and written into physical form by his companions. 

The original Arabic text of the Qur'an contains no flaws or contradictions, and has not been altered since its revelation. 

Actual 7th century Qur'ans, complete and intact, are on display in museums in Turkey and other places around the world. 

If all Qur'ans in the world today were destroyed, the original Arabic would still remain. This is because millions of Muslims, called "hafiz" (or "guardians") have memorized the text letter for letter from beginning to end, every word and every syllable. Also, chapters from the Qur'an are precisely recited from memory in each of the five formal prayers performed daily by hundreds of millions of Muslims throughout the world.