All perfect praise be to Allah, The Lord of the Worlds. I testify that there is none worthy of worship except Allah, and that Muhammad is His slave and Messenger.
It is proved that martyrs are alive and lead a life of comfort and ease in Paradise.
Allah Says (what means): {And never think of those who have been killed in the cause of Allah as dead. Rather, they are alive with their Lord, receiving provision.} [Quran 3: 169]
It is also proved in Saheeh Muslim that Masrooq said: “We asked ‘Abdullah Ibn Mas’ood about the meaning of the verse, who said: 'We asked about that.’ Ibn Mas’ood added: ‘The souls of martyrs live in the inside of green birds, who have their nests in chandeliers, hung from the throne of The Almighty. They go out freely in Paradise, then return to those chandeliers. Once their Lord (Allah) looked down at them and said: 'Do you wish something?' They answered: 'Which thing do we wish since we go out freely in Paradise'. He (The Exalted) asked that thrice. Then, when they believed that Allah will not leave them unless they ask for something. They said: 'O Lord! We desire that our souls be returned to our bodies so that we can be killed again. Then, when Allah saw (and He Knew that before) that they had no need, so they were left.' Al-Qurtubi said: “Only the martyrs’ food and comfort are hastened.” According to Ibn al-'Arabi, “there is a consensus among the Muslim Ummah on this point.”
Prophets are also alive, and their lives are more perfect than the lives of martyrs. There is agreement among scholars concerning this point.
As for the dead, in general, only their future position in Paradise is exposed to them if they are (by Allah's Favor) among its inhabitants. Then, it is kept till the Day of Resurrection.
Ibn ‘Umar narrated that the Prophet said: “When one among you dies, he is shown his position. If he is one of the people of Paradise, he is shown his place in Paradise; and if he is one of the people of Hellfire, he is shown his place in Hellfire. Then, it is said: “This is your position until Allah raises you from death on the Day of Resurrection.” [Al-Bukhaari and Muslim]
As for Prophets and martyrs hearing in graves, this is proved for all human beings, Muslims and non-Muslims, but this hearing is restricted only to the sound of footsteps of the living people when they leave the graves; i.e., after burying someone.
The Prophet said: “When a dead servant is put into his grave (buried) and his fellows (relatives and those who take part in burial) leave him, he hears the sound of their footsteps.” [Al-Bukhari and Muslim]
The Prophet addressed some killed people of the polytheists after the battle of Badr. The Companions asked: “O Messenger of Allah, are you calling out to people who have turned into rotten corpses?” The Prophet replied to them: “You do not hear what I say any better than they do.” [i.e. they also hear]
Qataadah said: “Allah, The Exalted, has breathed life into them till they can hear. The Prophet's saying is a form of rebuke, depreciation and wrath and to make them regret.”
Allah knows best.