Is there a noble prophetic hadith, according to the schools of Ahl al-Sunnah, whose central theme is that the Holy Qur'an has not been subjected to distortion?

The proof of the Qur'an's preservation from alteration is the Almighty's saying: (Indeed, it is We who sent down the Dhikr [i.e., the Qur’an] and, indeed, We will be its guardian). Muslims have unanimously agreed upon its preservation and its immunity from alteration, and whoever claims that alteration has occurred therein is a disbeliever.