What does islam say about grave? What happens after death in grave?
Human life can be divided into four phases:
1) The phase from the time when the souls were created collectively and divinely asked, “Am I not your Lord?” until the time when the spirit of the fetus in the mother’s womb is blown into it around four months and ten days of the pregnancy. We can also call this the pre-earthly soul period. No one remembers or knows his state in this period except those whom Allah has permitted.
2) The life on Earth. The body is a tool that has the physical conditions, and characteristics of the world and serves as a cover and a medium for the soul during the time it needs to stay in this world.
3) The period of life in the grave between death and the apocalypse. Accordingly, the life in the grave is between the life of this world and the life of the hereafter. This is also called the life of barzakh.
4) The life in the hereafter, which will begin with the resurrection and continue forever.
The life in the grave, which will begin as good or bad according to the answers given to the questions of two angels, Munkar and Nakir, is mentioned in the Book and the Sunnah.
Allah Almighty says: “In front of the Fire will they be brought, morning and evening: And (the sentence will be) on the Day that Judgment will be established: ‘Cast you the People of Pharaoh into the severest Penalty!’” It is understood that the torment mentioned in this verse, which is to occur before the Doomsday, is the torment in the grave.
When a person is put in the grave after death, two angels named Munkar and Nakir will come to him and ask, “Who is your Lord?”, “Who is your Prophet?”, and “What is your religion?” Those who have faith and good deeds will answer these questions correctly, and they will be shown Paradise by the opening of a door in their graves towards Paradise. The disbelievers and hypocrites, on the other hand, will not be able to answer these questions correctly, and the gates of Hell will be opened to them and they will be shown Hell, and painful and troubled life in the grave will begin for them.
The following is stated in the hadiths: “Indeed the grave is the first stage among the stages of the Hereafter. So if one is saved from it, then what comes after it is easier than it. And if one is not saved from it, then what comes after it is worse than it.”, and “The grave is but a garden from the gardens of Paradise, or a pit from the pits of the Fire.” Ibn Abbas (ra) narrates that the Messenger of Allah (saw) said while passing by the two graves, “They (their occupants) are being tormented, but they are not tormented for a grievous sin. One of them carried tales and the other did not keep himself safe from being defiled by urine. He then called for a fresh twig and split it into two parts, and planted them on each grave, and then said: Perhaps, their punishment way be mitigated as long as these twigs remain fresh.”
 Al-Aʿrāf, 7: 172. Al-Ghāfir, 40: 46. For the questioning in the grave see Muslim, Jannah, 17; al-Tirmidhī, Janā’iz, 70; Targhīb wa al-Tarhīb, III, 369. Al-Tirmidhī, Zuhd, 5; Ibn Maja, Zuhd, 32. Al-Tirmidhī, Qiyāmah, 26. Al-Bukhari, 4/55; Muslim, 2/34; Abu Dawūd, 1/11; al-Tirmidhī, 1/53.