Caution: Translations of Quran and Ḥadīth may lead to possible misapplications and misinterpretations. This site is intended for students of sacred knowledge that are proficient in comprehending classical Arabic and have a strong foundation in Islamic sciences. Also note that religious injunctions rely on several aspects beyond what one may glean through reading individual aḥādīth.
Qurʾān Bukhārī Muslim Nasāʾī Abū Dāwūd Tirmidhī Ibn Mājah Mālik Aḥmad Dārimī Ḥākim Ibn Ḥibbān Ṭabarānī Nasāʾī's Kubrá Bayhaqī al-Luʾluʾ wa-al-Marjān Ibn Rajab's Fifty Riyāḍ al-Ṣāliḥīn Aḥmad's Zuhd Suyūṭī
quran:21:49 –

Who fear their Lord unseen, while they are of the Hour apprehensive.  

those who fear their Lord in concealment, from people, that is, when they are in seclusion from them, and who, on account of the Hour, that is, ˹on account of˺ its terrors, are apprehensive, fearful.
القرآن:٢١:٤٩ –

الَّذِينَ يَخْشَوْنَ رَبَّهُمْ بِالْغَيْبِ وَهُمْ مِنَ السَّاعَةِ مُشْفِقُونَ  

{الذين يخشون ربهم بالغيب} عن الناس أي في الخلاء عنهم {وهم من الساعة} أي أهوالها {مشفقون} خائفون.

See similar narrations below:

Collected by Qurʾān
quran:23:57 –

Indeed, they who are apprehensive from fear of their Lord  

Surely those who, for fear of their Lord, are apprehensive, are fearful of His chastisement,
القرآن:٢٣:٥٧ –

إِنَّ الَّذِينَ هُمْ مِنْ خَشْيَةِ رَبِّهِمْ مُشْفِقُونَ  

{إن الذين هم من خشية ربهم} خوفهم منه {مشفقون} خائفون من عذابه.