Fiqh-us-Sunnah - 4.19

Hadith 4.19.1

On Invoking Allah Upon Witnessing Death, and Saying 'Inna lillahi wa inna ilayhi raja'un'

Saying: "Inna lillahi wa inna ilayhi raji'un" (We belong to Allah and truly to Him we shall Return) A believer should, at the death of a relative or a friend, invoke Allah and say: "Verily we belong to Allah, and truly to Him shall we return." The following reports show that to do so is commendable.
Ahmad and Muslim reported from Umm Salmah that she said: "I heard the Prophet, peace be upon him, saying: "If a servant of Allah is afflicted with a misfortune and says: Inna lillahi wa inna ilayhi raji'un, Allahumma ajirni fi musibati wa akhlif li khairan minha 'Verily we belong to Allah and truly to Him shall we return. O Allah! Protect me in this calamity that has befallen me and replace it with something better,' Allah will accept his prayer, grant him reward for his affliction, and replace it with something better." She added: "When Abu Salmah (her husband) died, I invoked Allah in the words taught to me by the Prophet, peace be upon him, and Allah did grant me someone better than he, i.e., (He gave me) the Messenger of Allah (as a husband)."
Tirmidhi reports from Abu Musa al-Ash'ari that the Prophet, peace be upon him, said: "When a child of a servant of Allah passes away, Allah says to the angels: 'Did you take the soul of My servant's child?' They say: 'Yes.' He, the Almighty, says: 'Did you take away the apple of my servant's eye?' They say: 'Yes.' He, the Almighty says: 'What did My servant say at this?' They say: 'He praised You and said: "Inna lillahi wa inna ilayhi raji'a un (Verily we belong to Allah and to Him shall we return)." At this Allah says: ' Build for My servant a mansion in Paradise and call it the House of Praise (bayt al-hamd)'." Tirmidhi says this is a sound hadith.
Bukhari has reported from Abu Hurairah that the Prophet, peace be upon him, said: "Allah, the Exalted and Glorious says: 'I have no better reward than Paradise for a believing servant of Mine who is patient and resigned when I take away one of his beloved, one among those he most cherishes in the world."
"Those who say, when afflicted with calamity, 'To Allah we belong, and to Him is our return,' are those on whom descend blessings from Allah, and mercy, and they are the ones who receive guidance." 55 Commenting on these verses of the Qur'an, Ibn Abbas said: "Allah, the Almighty and the Exalted, informs us that when a believer is patient and resigned after a misfortune visits him and invokes Allah, Allah will grant him three (good) merits: blessings, mercy, and guidance to the right path."