What can benefit the deceased after his death? Can he hear what the living say?
Praise be to Allaah.
The principle is that the dead do not hear the words of the living, because Allaah says (interpretation of the meaning): "… but you cannot hear those who are in graves." [Faatir 35:22] and "Verily, you cannot make the dead to hear…" [al-Naml 27:80]
When the Prophet SAW (peace and blessings of Allaah be upon him) addressed the slain kuffaar (disbelievers) after the Battle of Badr, Allaah caused them to hear his words, although they were at the bottom of the well in which they had been buried. This was a special case, as the scholars, may Allaah have mercy on them, have stated. (See Al-Aayaat al-Bayyinaat fi ‘adam Samaa’ al-Amwaat).
One should understand, that Islam has explained what actions on the part of the living may benefit the dead, and what may reach them in their graves. The Prophet SAW (peace and blessings of Allaah be upon him) said: "When a person dies, all his deeds come to an end except three: sadaqah jaariyah (ongoing charity, e.g. a waqf or endowment), beneficial knowledge (which he has left behind), or a righteous child who will pray for him." (Reported by al-Tirmidhi, no 1376; he said this is a saheeh hasan hadeeth)
The most important thing that will benefit your one after his/her death, and that you can do for him/her now that he/she is in grave, is to strive to pray for him/her and ask for forgiveness and mercy for him, and for Paradise and salvation from the Fire, and other good and beautiful du’aa’s (prayers).
Prayers for forgiveness offered by both sons and daughters of the deceased bring great benefits, as the Prophet SAW (peace and blessings of Allaah be upon him) said: "A man’s status will be raised in Paradise and he will ask, ‘How did I get here?’ He will be told, ‘By your son’s du’aa’s (prayers) for forgiveness for you." (Reported by Ibn Maajah, no 3660; see also Saheeh al-Jaami’, 1617)
Another thing that may reach the deceased is sadaqah (charity) given on his behalf, because ‘Aa’ishah (may Allaah be pleased with her) reported that a man said to the Prophet SAW (peace and blessings of Allaah be upon him): "My mother has passed away, and if she could have spoken, she would have given something in charity. Will she receive a reward if I give something on her behalf?" He said, "Yes." (Reported by al-Bukhaari, Fath, 1388)
Ibn ‘Abbaas (may Allaah be pleased with him and his father) reported that the mother of Sa’d ibn ‘Ubaadah (may Allaah be pleased with him and his father) died when he was away from her. He said: "O Messenger of Allaah, my mother has died and I am away from her. Will it benefit her anything if I give in charity on her behalf?" He said, "Yes." He said, "Then I ask you to be my witness that I am giving my garden al-Mikhraaf (so called because it bore so many dates) in charity on her behalf." (Reported by al-Bukhaari, Fath, 2756)
Abu Hurayrah reported that a man said to the Prophet SAW (peace and blessings of Allaah be upon him): "My father has died and left money behind. He did not make a wasiyyah (a will); will it expiate for his sins if I give some of it in charity on his behalf?" He said, "Yes." (Reported by al-Nisaa’i)
Sa’d ibn ‘Ubaadah said: "I said: ‘O Messenger of Allaah, my mother has died. Should I give charity on her behalf?’ He said, ‘Yes.’ I asked, ‘What kind of charity is best?’ He said, ‘Providing water.’" (Reported by al-Nisaa’i)
Other deeds that may also benefit the deceased are Hajj and ‘Umrah on their behalf, after the living person has first performed Hajj and ‘Umrah on his or her own behalf.
‘Abdullaah ibn Buraydah reported that his father (may Allaah be pleased with him) said: "While I was sitting with the Messenger of Allaah SAW (peace and blessings of Allaah be upon him), a woman came to him and said: ‘I gave my mother a slave-woman in charity, and now my mother has died.’ He said: ‘You have got your reward, and your right of inheritance has brought your gift back to you.’ She said, ‘O Messenger of Allaah, she still had one month to fast – can I fast it on her behalf?’ He said, ‘Fast it on her behalf.’ She said, ‘She never went to Hajj – can I perform Hajj on her behalf?’ He said, ‘Perform Hajj on her behalf.’" (Reported by Muslim, may Allaah have mercy on him, in his Saheeh, no. 1149)
This shows that it is also permissible to fast on behalf of the deceased.
Another thing that may benefit the deceased is to fulfil their nadhr (vow), because Ibn ‘Abbaas (may Allaah be pleased with him and his father) reported that a woman came to the Prophet SAW (peace and blessings of Allaah be upon him) and said: "My mother made a vow to perform Hajj but she died before she could do it. Can I perform Hajj on her behalf?" He said, "Yes, perform Hajj on her behalf. Don’t you think that if your mother owed a debt you would pay it off?" She said, "Yes." He said, "Then pay off what is owed to Allaah, for Allaah is more deserving of having vows fulfilled." (al-Bukhaari, al-Fath, 7315)
Another thing that may benefit the deceased is if his relative devotes a share to him of a sacrifice he offers. When the Prophet SAW (peace and blessings of Allaah be upon him) offered a sacrifice, he said: "In the name of Allaah, O Allaah, on behalf of Muhammad and the family of Muhammad" (reported by Muslim, no. 1967) – and the family of Muhammad included both the living and the dead.
One should avoid forbidden innovations (bid’ah) such as marking the fortieth day after death, or the passing of one year since the death, or gatherings for reciting al-Faatihah (the first chapter or soorah of the Qur’aan), doing forbidden acts at graves, and so on, deeds which are done by those who are ignorant and are imitated by others.
I ask Allaah to forgive your father and have mercy on him and on all the deceased Muslims, for He is the Forgiving, Most Merciful.