La ya'teehi albatilu min bayni yadayhi wala min khalfihi tanzeelun min hakeemin (surah Fussilat: 42)

Tafseer Tafheem-ul-Quran by Syed Abu-al-A'la Maududi

(41:42) Falsehood may not enter it from the front or from the rear. *52 It is a revelation that has been sent down from the Most Wise, the Immensely Praiseworthy.

Laa yaateehil baatilu mim baini yadaihi wa laa min khalfihee tanzeelum min Hakeemin Hameed

*52) "Falsehood . . . . from before it" means that none can succeed in proving anything wrong or any teaching false in the Qur'an by making a frontal attack on it; . . . . nor from behind it" means that nothing can be discovered till Resurrection which may be opposed to the truths and realities presented by the Qur'an; no new science, if it is really a "science", can be propounded, which may contradict the knowledge contained in the Qur'an; no new experiment or observation can be made to prove that the guidance given to man by the Qur'an in respect of the beliefs, morality, law, civilization or culture, and economic, social and political lift is wrong. That which this Book has declared as the Truth can never be proved to be falsehood and that which it has declared as falsehood can never be proved to be the truth. Furthermore, it also means that whether falsehood makes a frontal attack, or makes a surprise attack by deception, it cannot defeat the message which the Qur'an has brought. In spite of all sorts of open and secret machinations of the opponents the message will spread and none shall be able to defeat and frustrate it.