THE ‘ULAMĀ’ ARE unanimous that du‘ā’ for the dead benefits them and the reward of it reaches them. They cite as proof the saying of Allah 
: “And those who came after them say: ‘Lord, forgive us and our brothers who came before us into the faith.’” [1].
: “And those who came after them say: ‘Lord, forgive us and our brothers who came before us into the faith.’” [1].
[They also cite] other well-known verses in the same sense, and well-known hadiths such as the sayings of the Messenger of Allah 
: “Allah, forgive the people of Baqī‘ al-Gharqad” [2].and: “Allah, forgive our living and our dead.” [3].
: “Allah, forgive the people of Baqī‘ al-Gharqad” [2].and: “Allah, forgive our living and our dead.” [3].The ‘ulamā’ disagree as to whether the reward for recitation of the Qur’ān reaches the deceased. The well-known opinion of ash-Shāfi‘ī and a body of scholars is that it does not reach him. Imam Aḥmad ibn Ḥanbal and a body of scholars and a body of the colleagues of ash-Shāfi‘ī are of the opinion that the reward reaches him. The preferred view is that the reciter should say after his recitation: “O Allah, make the reward of what we have recited reach So-and-so.” But Allah knows best. It is mustaḥabb to praise the deceased and to mention his good deeds and traits.
We relate in the Ṣaḥīḥs of al-Bukhārī and Muslim from Anas 
who related that [he and some others] passed by a funeral and described [the deceased] as good, and the Messenger of Allah said: “It is inevitable.” Then they passed by another and they described him as bad. The Messenger of Allah said: “It is inevitable.” ‘Umar ibn al-Khaṭṭāb asked: “What is inevitable?” He said: “For the one whom you described as good, Paradise is inevitable; and for the one whom you described as bad, Hell-Fire is inevitable. You are the witnesses of Allah on the earth.” [4].
who related that [he and some others] passed by a funeral and described [the deceased] as good, and the Messenger of Allah said: “It is inevitable.” Then they passed by another and they described him as bad. The Messenger of Allah said: “It is inevitable.” ‘Umar ibn al-Khaṭṭāb asked: “What is inevitable?” He said: “For the one whom you described as good, Paradise is inevitable; and for the one whom you described as bad, Hell-Fire is inevitable. You are the witnesses of Allah on the earth.” [4].We relate in the Ṣaḥīḥ of al-Bukhārī that Abū al-Aswad related: “I once came to Madīnah and sat with ‘Umar ibn al-Khaṭṭāb . A funeral [procession] passed by and those in it described [the deceased] as good; and ‘Umar said: ‘It is inevitable.’ Then another passed by and those in it described [the deceased] as good and ‘Umar said: ‘It is inevitable.’ Then a third passed by and those in it described [the deceased] as bad and ‘Umar said: ‘It is inevitable.’ Abū al-Aswad asked: ‘What is inevitable, Leader of the Believers?’ He replied: ‘I have said what the Messenger of Allah said: “Any Muslim for whom four people testify, Allah will enter into Paradise.” We asked: “[What about] three [people]?” He said: “Or three.” We asked: “Two [people]?” He said: “Or two.” We did not ask him about one.’” [5].The hadiths in this regard are many. And Allah knows best.
. A funeral [procession] passed by and those in it described [the deceased] as good; and ‘Umar said: ‘It is inevitable.’ Then another passed by and those in it described [the deceased] as good and ‘Umar said: ‘It is inevitable.’ Then a third passed by and those in it described [the deceased] as bad and ‘Umar said: ‘It is inevitable.’ Abū al-Aswad asked: ‘What is inevitable, Leader of the Believers?’ He replied: ‘I have said what the Messenger of Allah said: “Any Muslim for whom four people testify, Allah will enter into Paradise.” We asked: “[What about] three [people]?” He said: “Or three.” We asked: “Two [people]?” He said: “Or two.” We did not ask him about one.’” [5].The hadiths in this regard are many. And Allah knows best.References
[1] Qur’ān 59:10.
[2] Muslim (974).
[3] Abū Dāwūd (3201).
[4] Al-Bukhārī (1367), Muslim (949), at-Tirmidhī (1058), and an-Nasā’ī (4/49–50).
[5] Al-Bukhārī (1368), at-Tirmidhī (1059), and an-Nasā’ī (4/51).