The Noble Quran is the eternal miracle of Prophet Muhammad . Every Prophet was supported with a miracle(s) and upon his death it disappeared, except Prophet Muhammad whose miracle remained, preserved and protected, namely the Book of Allah, His divine revealed Word. Allah Says (what means): "Falsehood cannot approach it from before it or from behind it." [Quran 41:42]
Allah clearly stated that the Quran is His Word, Saying (what means):
"And if any one of the polytheists seeks your protection, then grant him protection so that he may hear the words of Allah [i.e. the Quran]."[Quran 9:6], and in His Saying (which means): "Those who remained behind will say when you set out toward the war booty to take it, 'Let us follow you'. They wish to change the words of Allah." [Quran: 48:15] These two verses prove that the Quran is the Word of Allah and that He sent it down to Prophet Muhammad .
The Sunnah of the Prophet (his sayings) further proves this fact; Jaabir may Allah be pleased with him narrated: "The Prophet used to offer his message to people during the season of Hajj and say: "Is there a man who would take me to his tribe (i.e. to convey the message to them), because the (tribe of) Quraysh have prevented me from conveying the Word of Allah?" [Ahmad & At-Tirmithi]
There are many logical and substantial evidences proving this fact, such as the inability of the polytheists to come up with one single verse, let alone a whole chapter, that is similar to it. This is so, despite their eagerness and ambition to prove the Prophet wrong in what he was calling to, and their strong command of the Arabic language in which the Quran was revealed. Undoubtedly, this is evidence that the Quran is not made by or the words of humans.
The Quran contains news of past nations and other unseen matters which serve as great proof that it is the Word of Allah. When the Persians defeated the Romans in battle, the Quran addressed the issue and informed that the Romans would overcome the Persians in few years to come as Allah Says (what means): "The Romans have been defeated (i.e. By the Persians) in the nearest land. But they, after their defeat, will overcome." [Quran 30: 2-3]
Furthermore, the Quran consists of scientific miracles by highlighting certain scientific facts which were not discovered except fourteen centuries later, such as the Quran proving that there is a barrier between the salty water and fresh water where they meet preventing them from mixing, as Allah Says (what means): "He released the two seas (the two bodies of water: fresh and salt), meeting [side by side]. Between them is a barrier [so] neither of them transgresses." [Quran 55: 19-20] Modern science discovered this to be a fact.
The fact that tranquility and assurance can be found upon reading the Quran which is not felt when reading any other book, is yet another proof that it is the Word of Allah, as Allah Says (what means): "Those who have believed and whose hearts are assured by the mention of Allah. Unquestionably by the remembrance of Allah hearts are assured." [Quran 13: 28]
Furthermore, being cured by virtue of reading the Quran over a sick person can be added to the list of evidences proving it to be the Word of Allah. Allah Says (what means): "And We send down of the Quran that which is healing and mercy for the believers." [Quran 17: 82]
Lastly, the evidences proving the Quran to be the Word of Allah are too many to numerate in one article, and so we conclude with the saying of Al-Waleed Ibn Al-Mugheerah, one of the leaders of the polytheists who was requested to criticize and censure the Quran. After hearing parts of it from Prophet Muhammad he said: "What can I say? I swear by Allah! There is no man who knows poetry better than me, and it does not sound like anything I ever heard. The only thing I can say is that it has sweetness to it, and it is so appealing. It is so fruitful (to the heart) and abundant (in its benefits). Indeed, nothing rises above it in style, and it surely destroys anything that challenges it." [Al-Haakim & Al-Bayhaqi]
This is the Quran, the Word of Allah, which confounds humans' capabilities due to its inimitable style, justice and accuracy. The Quran still challenges people and people remain incapable of challenging it, and it remains the clear evidence from Allah against its enemies and opponents. All efforts to deny its authenticity have failed.