The Prophet (saas) announced that the Qur'an was revealed to man by Allah

during and after the time of the prophet (saas) there have been those who denied that the qur'an is a divine book. some of these people even went so far as to claim it was the prophet (saas) himself who had written it. yet, it is evident that the qur'an was not written by any human hand. the qur'an is the word of allah, and contains many miracles and is a superior wisdom, the like of which no human being could ever conceive. the prophet (saas) reminded people of this, and announced that the qur'an had been sent by allah. these are some of the verses that refer to this:

say: "the one who sent it down is he who knows all hidden secrets in the heavens and earth. he is ever-forgiving, most merciful." (surat al-furqan: 6)

say: "what do you think? if it is from allah and you reject it, who could be more misguided than someone entrenched in hostility to it?" (surah fussilat: 52)

those who allege that the qur'an was written by a human being are unaware of the miracles it contains and that its wisdom is from allah. in fact, the qur'an is such a book that not even all the people in the world and all the jinn together could have written it, let alone one man. the prophet (saas) was commanded to say the following on the subject:

say: "if both men and jinn banded together to produce the like of this qur'an, they could never produce anything like it, even if they backed each other up." (surat al-isra': 88)

do they say, "he has invented it?" say: "then produce a sura like it and call on anyone you can besides allah if you are telling the truth." (surah yunus: 38)

in another hadith, the prophet (saas) stated that the qur'an was the word of allah:

"honesty descended from the heavens and settled in the roots of the hearts of men (faithful believers), and then the qur'an was revealed and the people read the qur'an, (and learned from it) and also learned it from the sunnah. both qur'an and sunnah strengthened their (the faithful believers') honesty."41

the revelation of the book is from allah, the almighty, the all-wise.
(surat az-zumar: 1)

this is a book we have sent down to you so that you can bring mankind from the darkness to the light, by the permission of their lord, to the path of the almighty, the praiseworthy.
(surah ibrahim: 1)