The Quranic Dua for Calamity
إِنَّا لِلَّهِ وَإِنَّا إِلَيْهِ رَاجِعُونَ
Transliteration: Inna lillahi wa inna ilayhi raji'un
Meaning: "Indeed we belong to Allah, and indeed to Him we will return." — Quran 2:156
The Complete Dua When Afflicted with Calamity
اللَّهُمَّ أْجُرْنِي فِي مُصِيبَتِي، وَأَخْلِفْ لِي خَيْرًا مِنْهَا
Meaning: O Allah, reward me for my calamity and compensate me with something better than it.
Sahih Muslim 918
Dua for the Deceased
اللَّهُمَّ اغْفِرْ لَهُ وَارْحَمْهُ، وَعَافِهِ وَاعْفُ عَنْهُ
Meaning: O Allah, forgive him, have mercy on him, grant him well-being, and pardon him.
The Prophet's Promise
The Prophet Muhammad (peace be upon him) said: "No Muslim is afflicted with a calamity and says what Allah commanded (Inna lillahi wa inna ilayhi raji'un, Allahumma ajurni fi musibati...), except that Allah will reward him for his calamity and compensate him with something better." (Sahih Muslim 918)