Acording to following verse, preservation of Qur’an, its recitation and its clarification (Tafseer) is the responsibility of Allah:
Qur’an 75: 17.
إِنَّ عَلَيْنَا جَمْعَهُ وَقُرْآنَهُ
Saheeh: Indeed, upon Us is its collection [in your heart] and [to make possible] its recitation.
بے شک اس کا جمع کرنا اور پڑھا دینا ہمارے ذمہ ہے
Qur’an 75:18.
فَإِذَا قَرَأْنَاهُ فَاتَّبِعْ قُرْآنَهُ
Saheeh: So when We have recited it [through Gabriel], then follow its recitation.
پھر جب ہم ا سکی قرأت کر چکیں تو اس کی قرأت کا اتباع کیجیئے
Qur’an 75:19.
ثُمَّ إِنَّ عَلَيْنَا بَيَانَهُ
Saheeh: Then upon Us is its clarification [to you].
پھر بے شک اس کا کھول کر بیان کرنا ہمارے ذمہ ہے
The means of knowing the explanation of the words of the Qur’an that Allah taught His Messenger and the Messenger his Ummah by word and deed, is none but the Hadith and the Sunnah, The Hadith implies the traditions which the earliest followers passed on to the later generations about the sayings and acts of the Messenger on sound authority, and the Sunnah implies the way of life which became prevalent in the individual and collective life of the Muslims by the Holy Messenger’s oral and practical teaching, the details of which have been bequeathed by the former to the latter generations by reliable traditions as well as seen .by them practically in the life of the earliest followers. The person who refuses to acknowledge this means of knowledge, in fact, says that Allah after taking the responsibility of explaining the meaning of the Qur’an to His Messenger had, God forbid, failed to fulfill His promise. For this responsibility had not been taken to explain the meaning only to the Messenger in his personal capacity but for the purpose that the Ummah also be made to understand the meaning of the Divine Book through the agency of the Messenger. And as soon as the Hadith and the Sunnah are denied to be a source of law, it virtually amounts to saying that Allah has failed to carry out His responsibility. May Allah protect us froth such blasphemy! To the one who argues that many people had also fabricated Hadid, we would say that fabrication of Hadid itself is a major proof of the fact that in the beginning the entire Ummah gave the sayings and acts of the Holy Messenger (Upon whom be Allah’s peace) the status of law, otherwise why should the people who wanted to spread error have fabricated false ,Hadith. For only those coins are counterfeited which are current in the bazaar; nobody would print paper currency which had no value in the bazaar. Then, those who say such a thing perhaps do not know that this Ummah had seen to it from the very beginning that no falsehood was ascribed to the holy man whose sayings and acts had the status of law, and as the danger of ascribing false things to him increased, the well-wishers of the Ummah made greater and still greater efforts to distinguish the genuine from the counterfeit. The science of distinguishing the genuine from the false traditions is a unique science invented and developed only by the Muslims. Unfortunate indeed are those who without acquiring this science are being misled by the western orientalists to look upon the Hadith and the Sunnah as un-authentic and un-reliable and do not realize how grievously they are harming Islam by their foolhardiness.
Reference: Tafheem ul Qur’an