Surah Al-Kahf 18:5

مَّا لَهُم بِهِۦ مِنْ عِلْمٍ وَلَا لِـَٔابَآئِهِمْ ۚ كَبُرَتْ كَلِمَةً تَخْرُجُ مِنْ أَفْوَٰهِهِمْ ۚ إِن يَقُولُونَ إِلَّا كَذِبًا

They have no knowledge of it, nor had their fathers. Grave is the word that comes out of their mouths; they speak not except a lie.

Translation: Saheeh International

Tafsir

They do not have in this in this saying any knowledge nor did their fathers before them who also used to say this. Dreadful grave is the word that comes out of their mouths kalimatan ‘word’ is for specification and it explains the unidentified feminine person of the verb kaburat ‘dreadful’; …

Excerpt from Tafsir al-Jalalayn, commentary on 18:5, via Quran.com. The reader has the full commentary and 9 more tafsirs.