In the name of Allah, Most Gracious, Most Merciful.
And Salutations upon Prophet Muhammad, the Prophet of Mercy (صلى الله عليه وآله وسلم)
There are several proofs from Quran and authentic hadiths that those muslims who are in graves and Prophets [Peace be upon them] can not only hear but even reply from the grave and also become a Waseela. It is proven from authentic hadiths that even Non muslims can hear in graves but do not have capability to reply.
Proof from Al Quran # 1
Quran states: So Salih left them, saying: "O my people! I did indeed convey to you the message for which I was sent by my Lord: I gave you good counsel, but ye love not good counselors!"(Quran 7:79)
.
Here Salih (a.s) is addressing his dead people who had already been destroyed, had dead not heard then Nauzobillah this ayah of Quran would have been illogical, secondly what is the meaning of Salih (a.s)'s address?
Tafsir Ibn Kathir states under this ayah
هذا تقريع من صالح عليه السلام لقومه، لما أهلكهم الله بمخالفتهم إياه، وتمردهم على الله، وإبائهم عن قبول الحق، وإعراضهم عن الهدى إلى العمى، قال لهم صالح ذلك بعد هلاكهم، تقريعاً وتوبيخاً، وهم يسمعون ذلك، كما ثبت في الصحيحين: أن رسول الله صلى الله عليه وسلم لما ظهر على أهل بدر،
Translation: These were the words of admonishment which Salih exchanged with his nation after “ALLAH HAD DESTROYED THEM” for denying Him and also becoming renegades against Him, rejecting to accept the Haqq (truth) plus giving preference to misguidance over guidance. Hadrat Salih (a.s) said these words after they were “DESTROYED AND THEY HEARD THE WORDS TOO” In relevance to this It is narrated in the 2 books of Sahih (i.e. Bukhari and Muslim) that the Messenger (saw) defeated the kufaar in Badr … [then Imam Ibn Kathir mentions the sahih hadith in which Prophet clearly said that they (dead) hear better than you (alive)
[Tafsir Ibn Kathir under 7:79]
Click here for Arabic source
Proof # 2 from Quran
Quran states: Lo! those who ward off (evil), when a glamour from the devil troubleth them, they do but remember (Allah's Guidance) and behold them seers! (Quran 7:201).
Imam Ibn Kathir (rah) narrates under this ayah:.
أن شاباً كان يتعبد في المسجد، فهويته امرأة، فدعته إلى نفسها، فما زالت به حتى كاد يدخل معها المنزل، فذكر هذه الآية: { إِنَّ ٱلَّذِينَ ٱتَّقَوْاْ إِذَا مَسَّهُمْ طَـٰئِفٌ مِّنَ ٱلشَّيْطَـٰنِ تَذَكَّرُواْ فَإِذَا هُم مُّبْصِرُونَ } فخر مغشياً عليه، ثم أفاق فأعادها، فمات، فجاء عمر، فعزى فيه أباه، وكان قد دفن ليلاً، فذهب فصلى على قبره بمن معه، ثم ناداه عمر فقال: يا فتى
{ وَلِمَنْ خَافَ مَقَامَ رَبِّهِ جَنَّتَانِ }
فأجابه الفتى من داخل القبر: يا عمر قد أعطانيهما ربي عز وجل في الجنة مرتين..
Translation: A young boy used to do (a lot) of worship in Masjid, however one woman fell in love with him and she started to attract him towards herself until one day he got persuaded and came to her house, but he recalled this ayah: { Lo! those who ward off (evil), when a glamour from the devil troubleth them, they do but remember (Allah's Guidance) and behold them seers}, he fainted right over there, when he recovered he remembered the ayah again and fainted once again but this time he passed away. After his death Sayyidna Umar (ra) met his father being saddened at his death, (the boy) was buried during night, Umar (ra) took his companions along and visited his grave, he prayed there and “Called the Boy” saying: Whosoever feared to stand in front of his Lord then there are 2 gardens for him! Voice came from the grave O (YA) Omar (ra) Allah has granted me both the gardens
[Tafsir Ibn Kathir,Under 7:201]
Click here for Arabic source
Proofs from Authentic Hadiths :
Hadith #1
"The Messenger of Allah spoke to the People (buried) in the Well saying: "Have you found out that what your Lord had promised you is true?" then someone exclaimed: "Are you calling out to the dead!" The Prophet replied: "You do not hear better than they do, except they do not respond."
(Sahih Bukhari, Volume 2, Book 23, Number 452)
Hadith #2
Allah's Messenger (may peace be upon him) let the dead bodies of the unbelievers who fought in Badr (lie unburied) for three days. He then came to them and sat by their side and called them and said: O Abu Jahl b. Hisham, O Umayya b. Khalaf, O Utba b. Rab'ila, O Shaiba b. Rabi'a, have you not found what your Lord had promised with you to be correct? As for me, I have found the promises of my Lord to be (perfectly) correct. Umar listened to the words of Allah's Apostle (may peace be upon him) and said: Allah's Messenger, how do they listen and respond to you? They are dead and their bodies have decayed. Thereupon he (the Holy Prophet) said: By Him in Whose Hand is my life, what I am saying to them, even you cannot hear more distinctly than they, but they lack the power to reply. Then'he commanded that they should be buried in the well of Badr.
[Sahih Muslim, Hadith # 6869]
Note: Here the Prophet (Peace be upon him) said , even you cannot hear more distinctly than they , Hence it proves that even Kafirs who are Dead can hear more clearly then alive can or equally let alone be Muslims and Prophets (aleh islam).But Kafirs cannot reply back according to this hadith, Where as muslims have the ability to reply as proved above and will be proved further.
.Hadith #3
Narrated Ibn Shihab:These were the battles of Allah's Apostle (which he fought), and while mentioning (the Badr battle) he said, "While the corpses of the pagans were being thrown into the well, Allah's Apostle said (to them), 'Have you found what your Lord promised true?" 'Abdullah said, "Some of the Prophet's companions said, "O Allah's Apostle! You are addressing dead people.' Allah's Apostle replied, 'You do not hear what I am saying, better than they.'
[Sahih Bukhari, Book 59, Number 360]
Hadith #4
Allah has declared it forbidden for the earth to eat the bodies of the prophets. So the prophets are living and they receive their sustenance
References
►Ibn Majah narrated this sahih (sound) hadith in his Sunan, b. of jana'iz (funerals) ch.65 (1:524#1636-7), b. of iqamat-us-salat was-sunnah fiha (establishing prayer and its sunnahs) ch.79 (1:345#1085);
► Abu Dawud, Sunan, b. of salat (prayer) 1:275 (#1047);
►Nasa'i, Sunan, b. of jumu'ah (Friday prayer) 3:92;
►Ahmad bin Hambal Musnad (4:8);
► Ibn Hibban, as-Sahih (3:191#910);
►Darimi, Sunan (1:307#1580);
► Ibn Khuzaymah, as-Sahih (3:118#1733);
►Ibn Abi Shaybah, al-Musannaf (2:516);
►Hakim, al-Mustadrak (1:278);
►Tabarani, al-Mu'jam-ul-kabir (1:217#589); and► Bayhaqi in as-Sunan-ul-kubra (3:249). Hadith #5 (Sahaba believed that they enjoyed the company of others after death)
Click Here to read more Proofs from Sahih hadiths on life of Prophets [aleh islam] in graves
Hadith #6,
Narrated Abu Sa'id Al-Khudri : Allah's Apostle said, "When the funeral is ready (for its burial) and the people lift it on their shoulders, then if deceased is a righteous person he says, 'Take me ahead,' and if he is not a righteous one then he says, 'Woe to it (me)! Where are you taking it (me)?' And his voice is audible to everything except human beings; and if they heard it they would fall down unconscious."
(Sahih Bukhari, Volume 2, Book 23, Number 462
,This shows that the Dead can not only hear us, but they are also aware of what is happening in this world. And their voice is audible to everything except human beings.
Hadith #7
The Prophet [salehalawaalihi wasalam] said :"My life is a great good for you, you will relate about me and it will be related to you, and my death is a great good for you, your actions will be presented to me (in my grave) and if I see goodness I will praise Allah, and if see other than that I will ask forgiveness of him (for you)."
References for above hadith:
►Qadi `Iyad cites it in "al-Shifa" (1:56 of the Amman edition)
► Suyuti said in his "Manahil al-safa fi takhrij ahadith al-shifa" (Beirut 1988/1408) p. 31 (#8):
►"Ibn Abi Usama cites it in his Musnad from the hadith of Bakr ibn `Abd Allah al-Mazni,
►al-Bazzar from the hadith of Ibn Mas`ud with a sound (sahih) chain.
►It is cited in Subki's Shifa' al-siqâm fi ziyarat khayr al-anâm
[The Healing of the Sick Concerning the Visit of the Best of Creation], where he mentions that Bakr ibn Abd Allah al-Mazini reported it, and Ibn al-Jawzi mentions it through Bakr and then again through Anas ibn Malik in the penultimate chapter of the penultimate section of al-Wafa, both huffaz without giving the isnad.
Ibn al-Jawzi statement on hadith
However, Ibn al-Jawzi specifies in the introduction of al-Wafa that he only included sound traditions in his book.
.
He also mentions the version through Aws ibn Aws: "The actions of human beings are shown to me every Thursday on the night of (i.e. preceding) Friday."
.
►See also FatH al-Bâri 10:415,
►al-Mundhiri's Targheeb wa al-Tarheeb 3:343, ►and Ahmad 4:484
Reference: https://islamtreasure.blogspot.com/2011/06/dead-can-hear-from-graves-proof-from.html