إِنَّهُ لَقَوْلٌ فَصْلٌ (this is a decisive word..At-Tariq 86:13 ⧉) In other words, the Qur'an is truly a Decisive Word that decides between truth and falsehood, and there is no room for any doubt in it.
Sayyidna ` Ali ؓ says that he heard the Holy Prophet ﷺ as saying about the Holy Qur'an:
کتاب فیہ خبرما قبلکم و حکم مابعدکم وھو الفصل لیس بلھزل
'[ It is ] a book which describes the stories of past communities and [ it contains ] injunctions for future generations. It is truly a Decisive Word. It is no joke.'