قَدۡ خَسِرَ الَّذِيۡنَ كَذَّبُوۡا بِلِقَآءِ اللّٰهِؕ حَتّٰٓى اِذَا جَآءَتۡهُمُ السَّاعَةُ بَغۡتَةً قَالُوۡا يٰحَسۡرَتَنَا عَلٰى مَا فَرَّطۡنَا فِيۡهَا ۙ وَهُمۡ يَحۡمِلُوۡنَ اَوۡزَارَهُمۡ عَلٰى ظُهُوۡرِهِمۡؕ اَلَا سَآءَ مَا يَزِرُوۡنَ(الأنعام :31)
Qad khasira allatheena kaththaboo biliqai Allahi hatta itha jaathumu alssa'atu baghtatan qaloo ya hasratana 'ala ma farratna feeha wahum yahmiloona awzarahum 'ala thuhoorihim ala saa ma yaziroona
Sahih International:
Those will have lost who deny the meeting with Allah, until when the Hour [of resurrection] comes upon them unexpectedly, they will say, "Oh, [how great is] our regret over what we neglected concerning it," while they bear their burdens on their backs. Unquestionably, evil is that which they bear.
يَسۡـَٔـــلُوۡنَكَ عَنِ السَّاعَةِ اَيَّانَ مُرۡسٰٮهَا ؕ قُلۡ اِنَّمَا عِلۡمُهَا عِنۡدَ رَبِّىۡ ۚ لَا يُجَلِّيۡهَا لِوَقۡتِهَاۤ اِلَّا هُوَۘ ؕ ثَقُلَتۡ فِى السَّمٰوٰتِ وَالۡاَرۡضِؕ لَا تَاۡتِيۡكُمۡ اِلَّا بَغۡتَةً ؕ يَسۡـــَٔلُوۡنَكَ كَاَنَّكَ حَفِىٌّ عَنۡهَا ؕ قُلۡ اِنَّمَا عِلۡمُهَا عِنۡدَ اللّٰهِ وَلٰـكِنَّ اَكۡثَرَ النَّاسِ لَا يَعۡلَمُوۡنَ(الأعراف :187)
Yasaloonaka 'ani alssa'ati ayyana mursaha qul innama 'ilmuha 'inda rabbee la yujalleeha liwaqtiha illa huwa thaqulat fee alssamawati waalardi la tateekum illa baghtatan yasaloonaka kaannaka hafiyyun 'anha qul innama 'ilmuha 'inda Allahi walakinna akthara alnnasi la ya'lamoona
Sahih International:
They ask you, [O Muhammad], about the Hour; when is its arrival? Say, "Its knowledge is only with my Lord. None will reveal its time except Him. It lays heavily upon the heavens and the earth. It will not come upon you except unexpectedly." They ask you as if you are familiar with it. Say, "Its knowledge is only with Allah, but most of the people do not know."
اَفَاَمِنُوۡۤا اَنۡ تَاۡتِيَهُمۡ غَاشِيَةٌ مِّنۡ عَذَابِ اللّٰهِ اَوۡ تَاۡتِيَهُمُ السَّاعَةُ بَغۡتَةً وَّ هُمۡ لَا يَشۡعُرُوۡنَ(يوسف :107)
Afaaminoo an tatiyahum ghashiyatun min 'athabi Allahi aw tatiyahumu alssa'atu baghtatan wahum la yash'uroona
Sahih International:
Then do they feel secure that there will not come to them an overwhelming [aspect] of the punishment of Allah or that the Hour will not come upon them suddenly while they do not perceive?
هَلۡ يَنۡظُرُوۡنَ اِلَّا السَّاعَةَ اَنۡ تَاۡتِيَهُمۡ بَغۡتَةً وَّهُمۡ لَا يَشۡعُرُوۡنَ(الزخرف :66)
Hal yanthuroona illa alssa'ata an tatiyahum baghtatan wahum la yash'uroona
Sahih International:
Are they waiting except for the Hour to come upon them suddenly while they perceive not?
Complete Indexing of Quran Topics
We have indexed and found 4 verses about or related to (including the word(s)) "Hour, All of a sudden it is on them".
For your information, the verses as described above: