Very few we know what happens in grave after completion of burial process.
As we still didn't die have many imagination, thinking, believe & disbelief, someone has more or less ideas, or distorted ideas, false ideas. But i quoted that Persons speech 1450 years back what he told proved as true, rest will be proved before coming doomed day. He is Prophet Muhammad (pbuh) and what he said about after death life will be found true if we trust those or not. Even who kept enmetiy with him never could to call him liar. In below post I added his two hadith (speech of Prophet Muhammad (pbuh) ] from many hadiths about grave. Here he said some what happens inside grave.
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Two angels who are engaged for questioning to all human being from beforehand come to him and ask him what was his believe in in this world, who was his Lord? what was his religion ? and who was his Prophet? If he gives satisfied answer, that is really true , hearing that angels get happy & arrange many rewards from Allah but if he can not give satisfied answer properly severe punishment and painful beating starts on him. They beat with iron hammer, those hammers are so powerful it is said if those hammer applied on mountain, mountain would turned into dust.
Source: hadith's book & islamqa.info
Hazrat Anas (Radiallahoanho) narrates The Prophet Muhammad (ﷺ) said, "When a human being is laid in his grave and his companions return and he even hears their foot steps, two angels (Malayka) come to him and make him sit and ask him: What did you use to say about this man, Muhammad ? He will say: I testifying that he is Allah's slave and His Apostle. Then it will be said to him, 'Look at your place in the Hell-Fire. Allah has given you a place in paradise instead of it.' " The Prophet (ﷺ) added, "The dead person will see both his places. But a non-believer or a hypocrite will say to the angels, 'I do not know, but I used to say what the people used to say! It will be said to him, 'Neither did you know nor did you take the guidance (by reciting the Qur'an).' Then he will be hit with an iron hammer between his two ears, and he will cry and that cry will be heard by whatever approaches him except human beings and jinns."
Hadith book of Bukhari
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Dear brothers there're many hadiths about grave life, i told two only.