Tafsir of An-Naba' 78:18

The Day when the Trumpet will be blown, and you shall come forth in crowds. Mujahid said, "Groups after groups.'' Ibn Jarir said, "This means that each nation will come with its Messenger. It is similar to Allah's statement,

يوم ندعوا كل أناس بٳممهم

The Day when We shall call together all human beings with their Imam. (17:71)'' Al-Bukhari reported concerning the explanation of Allah's statement,

يوم ينفخ فى الصور فتٲتون أفواجا

Abu Hurayrah said that the Messenger of Allah said,

ما بين النفختين أربعون

That which is between the two blowings is forty. Someone asked, "Is it forty days, O Abu Hurayrah'' But he (Abu Hurayrah) refused to reply, saying "no comment.'' They then asked, "Is it forty months'' But he (Abu Hurayrah) refused to reply, saying "no comment.'' They asked again, "Is it forty years'' But he (Abu Hurayrah) refused to reply, saying "no comment.'' (Abu Hurayrah added:) "Then the Prophet went on to say,

ثم ينزل الله من السماء ماء فينبتون كما ينبت البقل ليس من اﻻنسان شيء إﻻ يبلى إﻻ عظما واحدا وهو عجب الذنب ومنه يركب الخلق يوم القيامة

Then Allah will send down a rain from the sky and the dead body will sprout just as a green plant sprouts. Every part of the last person will deteriorate except for one bone, and it is the coccyx bone (tailbone). From it the creation will be assembled on the Day of Judgement.'' Allah says,

وفتحت السماء فكانت أبوابا