﴿ وَإِذَا قِيلَ إِنَّ وَعْدَ ٱللَّهِ حَقٌّۭ وَٱلسَّاعَةُ لَا رَيْبَ فِيهَا قُلْتُم مَّا نَدْرِى مَا ٱلسَّاعَةُ إِن نَّظُنُّ إِلَّا ظَنًّۭا وَمَا نَحْنُ بِمُسْتَيْقِنِينَ ﴾

“for when it was said, ‘Behold, God’s promise always comes true, and there can be no doubt about [the coming of] the Last Hour’ - you would answer, ‘We do not know what that Last Hour may be: we think it is no more than an empty guess, and [so] we are by no means convinced!’””

Please check ayah 45:37 for complete tafsir.