Quran 45:32 from Surah Al-Jaathiya on Divine Marvels.
وَإِذَا قِيلَ إِنَّ وَعۡدَ ٱللَّهِ حَقّٞ وَٱلسَّاعَةُ لَا رَيۡبَ فِيهَا قُلۡتُم مَّا نَدۡرِي مَا ٱلسَّاعَةُ إِن نَّظُنُّ إِلَّا ظَنّٗا وَمَا نَحۡنُ بِمُسۡتَيۡقِنِينَ
English translation: And when it was said indeed (the) Promise (of) Allah (is) true and the Hour (there is) no doubt about it you said Not we know what the Hour (is) Not we think except an assumption and not we (are) convinced
Transliteration: wa-idha qila inna wa'da al-lahi haqqun wal-sa'atu la rayba fiha qul'tum ma nadri ma al-sa'atu in nazunnu illa zannan wama nahnu bimus'tayqinina