﴿ لَّا يَأْتِيهِ ٱلْبَٰطِلُ مِنۢ بَيْنِ يَدَيْهِ وَلَا مِنْ خَلْفِهِۦ ۖ تَنزِيلٌۭ مِّنْ حَكِيمٍ حَمِيدٍۢ ﴾

“no falsehood can ever attain to it openly, and neither in a stealthy manner, [since it is] bestowed from on high by One who is truly wise, ever to be praised.”

falsehood cannot approach it from before it or from behind it in other words there is no scripture before it or after it that contradicts it; it is a revelation from One Wise Praised that is to say from God the One Who is praised in His affair.