When the son of Adam dies, his body disintegrates and vanishes apart from the tailbone, which is a bone at the base of the spine. When the Resurrection begins, Allaah will cause the bodies to grow by means of rain from the earth which will make these bones grow until each person’s body is restored to the way it was before he died. 

It was narrated that Abu Hurayrah (may Allaah be pleased with him) said: “The Messenger of Allaah (peace and blessings of Allaah be upon him) said, ‘What is between the two Trumpet-blasts will be forty.’ Somebody asked, ‘Forty days?’ But I could not answer. Then he asked, ‘Forty months?’ But I could not answer. Then he asked, ‘Forty years?’ But I could not answer.” Abu Hurayrah added, “Then (after this period) Allah will send water from the sky and then the dead bodies will grow like vegetation grows. There is nothing of the human body that does not decay except one bone; that is the little bone at the end of the coccyx from which the human body will be recreated on the Day of Resurrection.” 

(Narrated by al-Bukhaari, 4651; Muslim, 2955). 

Al-Nawawi said: 

“The Prophet (peace and blessings of Allaah be upon him) said, ‘What is between the two Trumpet-blasts will be forty.’ Somebody asked, ‘Forty days?’ But I could not answer…” What is meant is that he refused to specify whether it would be forty days, or years, or months. Rather what he was sure of was that it would be just forty. It is explained in another report narrated by someone other than Muslim, which says that it will be forty years. 

The phrase “the little bone at the end of the coccyx” refers to the small bone at the base of the spine, which is the end of the coccyx. This is the first part of a person that is created, and it is what will be left of him so that he will be created anew from it. 

Sharh Muslim, 18/92 

When a person comes forth from his grave and is gathered and brought to account, his body will remain the same as it was before he died. Then when the people of Paradise enter Paradise and the people of Hell enter Hell, Allaah will change their forms. 

Description of the people of Hell:

It was narrated from Abu Hurayrah that the Prophet (peace and blessings of Allaah be upon him) said: “The distance between the shoulders of the kaafir [in Hell] will be that of three days’ swift travelling.” (Narrated by al-Bukhaari, 6186; Muslim, 2852). 

It was narrated that Abu Hurayrah said: The Messenger of Allaah (peace and blessings of Allaah be upon him) said: “The molar of the kaafir – or the eyetooth of the kaafir – will be like Uhud, and his skin will be as thick as three days’ travelling.” (Narrated by Muslim, 2851). 

Description of the people of Paradise:

It was narrated that Abu Hurayrah (may Allaah be pleased with him) said: The Messenger of Allaah (peace and blessings of Allaah be upon him) said: “The first group to enter Paradise will look like the moon when it is full; then those who follow them will look like the brightest star in the sky. They will not urinate or defecate, spit or blow their noses. Their combs will be of gold, their sweat will be musk, their incense burners will be of aloes-wood. Their wives will be al-hoor al-‘iyn and they will all look alike, like their father Adam, sixty cubits tall.” (Narrated by al-Bukhaari, 3149; Muslim, 2834) 

It was narrated from Mu’aadh ibn Jabal that the Prophet (peace and blessings of Allaah be upon him) said: “The people of Paradise will enter Paradise hairless and beardless, with kohl-rimmed eyes, all thirty or thirty-three years old.” (Narrated by al-Tirmidhi, 2545). 

This hadeeth was classed as saheeh by Shaykh al-Albaani in Saheeh al-Jaami’, 8072. 

And Allaah knows best.