Please allow me to ask you the following question which I have been asked but I could not answer.
When someone dies, is he either tortured in the grave or on the Day of Reckoning? My question is on this part is; When the Messenger, sallallaahu ‘alayhi wa sallam, was taken up to the seven heavens, he saw different kinds of punishment. My question is: How did he see these different kinds of torture although the Day of Resurrection and Reckoning has not commenced yet? How are they being punished while the Day of Resurrection has not commenced yet?

All perfect praise be to Allaah, The Lord of the Worlds. I testify that there is none worthy of worship except Allaah, and that Muhammad, sallallaahu ‘alayhi wa sallam, is His Slave and Messenger.

The occurrence of the torment of the grave before the Day of Reckoning has been established with full certainty. Also, there is no connection between them. So whoever deserves the punishment of the grave, he will be certainly punished there. Then in the Hereafter he will face what is decreed for him as Imaam At-Tahaawi explained.

This can be clearly explained in the verse where Allaah The Almighty Says about Pharaoh (what means): {And the people of Pharaoh were enveloped by the worst of punishment. The Fire, they are exposed to it morning and evening. And the Day the Hour appears [it will be said], "Make the people of Pharaoh enter the severest punishment.} [Quran 40:45-46]

Consequently, it becomes clear now that the torment of the grave does not depend in any way on the punishment of people on the Day of Reckoning. Moreover, there is no problem in the occurrence of the torment of the grave before the Day of Reckoning i.e. in the realm of Al-Barzakh and before the beginning of the Hour.

There is evidence that prove that the torment of the grave will occur before the Reckoning, some of which are as follows:

It was narrated that the Messenger of Allaah, sallallaahu ‘alayhi wa sallam, once passed by two graves and said: “These two persons are being tortured not for a major sin (to avoid). One of them never saved himself from being soiled with his urine, while the other used to go about with calumnies (to make enmity between friends).”  [Al-Bukhari and Muslim]

Furthermore, it was mentioned in a Hadeeth that when the disbeliever says (to the angels who question him in the grave), “I do not know”, it will be said to him, “Neither did you know nor did you take the guidance (by reciting the Quran).” Then he will be hit with an iron hammer between his two ears. [Al-Bukhari]

Also, we have to know that the Messenger of Allaah, sallallaahu ‘alayhi wa sallam, is truthful in all what he has said, for Allaah The Almighty Says (what means): {Nor does he speak from [his own] inclination. It is not but a revelation revealed.} [Quran 53:3-4]

Moreover, Allaah The Almighty informs him with whatever He wills of the matters of the Unseen, as He Says (what means): {[He is] Knower of the Unseen, and He does not disclose His [knowledge of the] Unseen to anyone. Except whom He has approved of messengers.} [Quran 72:26-27]

Allaah Knows best.