When offering condolences about the plight of a relative, friend or acquaintance, it is mustahab (preferable) to make du’a similar to the following du’a for your deceased brother. This is a du’a which Rasulullah [Sallallahu álayhi wa sallam] recited to Ummu Salamah [Radiallahu anha] at the death of her husband:
الّلهمَّ اغْفِرْ لأَبِى سَلَمَةَ وَارْفعْ دَرَجَتَهُ فِى الْمَهْدِيِّينَ وَاخْلُفْهُ فِى عَقِبِهِ فِى الْغَابِرِيْنَ وَاغْفَرْلَنَا وَلَهُ يَا رَبَّ الْعَالَمِينَ وَافْسَحْ لَهُ فِى قَبْرِهِ وَنَوَّرْ لَهُ فِيهِ
“O Allah! Forgive Abu Salamah, elevate his status among the guided people and look after the family that he left behind. O Lord of the universe! Forgive us and him, comfort him in his grave and lighten his stay (in the grave).” [Sahih Muslim]
It is desirable that your conversation with the bereaved person be aimed at lightening the effect of the calamity. This could be done by mentioning the reward of patience over that calamity, the transitory nature of life on earth and that the hearafter is an everlasting abode.
In this respect, it is desirable certain verses of Qur’an that are connected to that, or some of the well-spoken condolences if our ancestors. You may mention virtues such as the following:
وَبَشِّرِ ٱلصَّـٰبِرِينَ (١٥٥) ٱلَّذِينَ إِذَآ أَصَـٰبَتۡهُم مُّصِيبَةٌ۬ قَالُوٓاْ إِنَّا لِلَّهِ وَإِنَّآ إِلَيۡهِ رَٲجِعُونَ (١٥٦) أُوْلَـٰٓٮِٕكَ عَلَيۡہِمۡ صَلَوَٲتٌ۬ مِّن رَّبِّهِمۡ وَرَحۡمَةٌ۬ۖ وَأُوْلَـٰٓٮِٕكَ هُمُ ٱلۡمُهۡتَدُونَ
(1) “Give glad tidings to those who patiently endure, who say when afflicted with a calamity: “To Allah we belong and to Him we return.” They are those on whom (descend) blessings and mercy from their Lord, and they are the ones who receive guidance.” [Surah Al-Baqarah: 155-157]
كُلُّ نَفۡسٍ۬ ذَآٮِٕقَةُ ٱلۡمَوۡتِۗ وَإِنَّمَا تُوَفَّوۡنَ أُجُورَڪُمۡ يَوۡمَ ٱلۡقِيَـٰمَةِۖ فَمَن زُحۡزِحَ عَنِ ٱلنَّارِ وَأُدۡخِلَ ٱلۡجَنَّةَ فَقَدۡ فَازَۗ وَمَا ٱلۡحَيَوٰةُ ٱلدُّنۡيَآ إِلَّا مَتَـٰعُ ٱلۡغُرُورِ
(2)”Every soul shall have a taste of death and only on the Day of the Judgement shall you be paid your full recompense. Only those who are saved from the fire and admitted to Paradise (Jannah) will have attained the object (of life). For the life of this world is but good and chattels of deception.” [Surah Áala Imran: 185]
كُلُّ مَنۡ عَلَيۡہَا فَانٍ۬ (٢٦) وَيَبۡقَىٰ وَجۡهُ رَبِّكَ ذُو ٱلۡجَلَـٰلِ وَٱلۡإِكۡرَامِ
(3) “All that is on earth will persish, but face of your Lord will abide (forever), full of Majesty, Bounty and Honour” [Surah Ar-Rahman: 26-27]
You may even mention ahadith of Rasulullah [Sallallahu álayhi wa sallam] such as the following:
اللَّهُمَّ آجِرْنِى فِى مُصِيبَتِى وَأَخْلِفْ لِى خَيرًا مِنْها
Allahumma aajur ni fee museebati wa akhlif li khairan minha.
(1) “O Allah! Reward me in my calamity and replace my loss with a better one. [Sahih Muslim]
أِنَّ للَّه مَا أَخَذَ وَلَهُ مَا أَعْطَى وَكُلُّ شَيْءٍ عِنْدَهُ بِأَجَلٍ مُسَمًّى
(2) “Indeed! Whatever Allah gives or takes belongs to him and everything is predestined by Him. [Sahih Bukhari & Sahih Muslim]
أِنَّ الْعَينَ تَدْمَعُ وَالْقَلْبُ يَحْزَنُ وَلَا نَقُولُ مَا يَرْضَى رَبُّنَا وَأِنَّا بِفِرَاقِكَ يَا أَبْرَاهِيمُ لَحْزُونُونَ
(3) When Rasulullah [Sallallahu álayhi wa sallam] mourned the death of his son, Ibrahim, he said the above which translates as : “My ears are tearful. My heart is full of anguish, but we will only say what pleases our Lord. O Ibrahim! We are indeed grieved over your separation.” [Sahih Bukhari & Sahih Muslim]
Also, it is very appropriate to use some of the sayings of the pious predecessors in this regard.
(1) Sayyiduná ‘Umar Ibn Al-Khattab [Radiallahu anhu] used to say, “Everyday we are told so and so has just died. Most definitely, one day it will be said: ‘Umar has died.”
(2) The Khalifa ‘Umar Ibn ‘Abdul Aziz [Rahimahullah] said, “The person who has none of hos forefathers, between him and Adam [álayhis salam] alive, is indeed deep-rooted in death.”
(3) The illustrious Tábi’í, Hasan Basri [Rahimahullah] said, “O son of Adam! You are nothing but mere days. Whenever a day passes away, a part of you also passes away.”
(4) He also said, “Allah ordained that the ultimate resting place of the believers will be paradise, no less”
(5) Hasan Basri’s [Rahimahullah] student Malik Ibn Dinar [Rahimahullah] said, “The wedding of the one who fears Allah will be on the day of Judgement.”
A poet said:
We rejoice at the passage of days;
Whereas each day that passes brings us closer to death.
Another poet said in this regard:
We dont offer condolences because we are certain
Of life, but because it is the practice of our Religion;
For, the consoled and the consoling may live today
Tomorrow though they will vanish away.
A suitable poem in this regard is:
We die and live every night and day (by sleeping);
One day we will die and move away.
Another poem describes how oblivious humans can be to death:
We in this world are like passengers on a ship of load;
We think it still, but running is the boat.
I have quoted all these appropriate mourning quotations because I have witnessed many people engaging in discussions that do not befitt such a sad occasion. This adds to the distress and anguish of the bereaved. This is also contrary to the style and etiquette of Islam.
My comments: It would be better if more knowledgeable brother(s) are left to advise those close to the deceased to observe patience.