Allah (ﷻ) says:
الَّذِينَ إِذَا أَصَابَتْهُم مُّصِيبَةٌ قَالُوا إِنَّا لِلَّهِ وَإِنَّا إِلَيْهِ رَاجِعُون (156)
Who, when afflicted with calamity, say: "Truly! To Allâh we belong and truly, to Him we shall return." (156) They are those on whom are the Salawât (i.e. who are blessed and will be forgiven) from their Lord, and (they are those who) receive His Mercy, and it is they who are the guided-ones. (157)
(Surah Al Baqarah 156-157)
Supplication when a calamity strikes
The Prophet (ﷺ) said: When a calamity strikes one of you, then let him say:
إِنَّا لِلهِ وَإِنَّا إِلَيْهِ رَاجِعُونَ ، اللَّهُمَّ أْجُرْنِي فِي مُصِيبَتِي ، وَاخْلُفْ لِي خَيْرًا مِنْهَا
Innaa lillaahi wa innaa ilayhi raaji‛oon, allaahumma’ jurnee fee muṣeebatee, wakhluf lee khayran minhaa
To Allah we belong and unto Him is our return. O Allah, recompense me for my affliction and replace it for me with something better
(Jami` at-Tirmidhi 3511)
Allah will give him reward for affliction, and would give him something better than it in exchange.
(Sahih Muslim 918)