The Quran

وَما كانَ هٰذَا القُرآنُ أَن يُفتَرىٰ مِن دونِ اللَّهِ وَلٰكِن تَصديقَ الَّذي بَينَ يَدَيهِ وَتَفصيلَ الكِتابِ لا رَيبَ فيهِ مِن رَبِّ العالَمينَ

Muhammad Asad

Now this Qur'an could not possibly have been devised by anyone save God: nay indeed,¹ it confirms the truth of whatever there still remains [of earlier revelations] and clearly spells out the revelation [which comes] - let there be no doubt about it - from the Sustainer of all the worlds.²

Lit., "but" (wa-lakin)- a stress on the impossibility of any assertion to the contrary.
The above passage has a twofold significance: firstly, the wisdom inherent in the Qur'an precludes any possibility of its having been composed by a human being; and, secondly, the Qur'anic message is meant to confirm, and give a final formulation to, the eternal truths which have been conveyed to man through a long succession of prophets: truths which have subsequently been obscured through wrong interpretation, deliberate omissions or interpolations, or a partial or even total loss of the original texts. For an explanation of the phrase ma bayna yadayhi, rendered by me in this context as "whatever there still remains [of earlier revelations]", see surah 3, note 3.