When will Death be slaughtered? What will be the condition of those who committed major sin, in al-barzakh?
Question

                When Death will be brought in the form of a ram and slaughtered before the people of Paradise and Hell, and it will be said to both of them, “It is eternal; there is no more death,” will that be after those of the ummah of Muhammad who committed major sins have been brought out of the Fire, or before that? I am also wondering: when those who committed major sins are questioned in the grave, will they answer the questions of Munkar and Nakeer correctly, or will they say, I do not know? Will they be shown their place in Paradise or Hell?
Praise be to Allah.Firstly:
What should be said is that the slaughter of Death will not happen until the people of Paradise have settled in Paradise, and the people of the Fire have settled in Hell. This implies that the slaughter of Death will not happen before those who professed the oneness of Allah have been brought forth from the fire of Hell, because the words are addressed to the people of Paradise and the people of Hell, and those who professed the oneness of Allah cannot be described as people of Hell when they are going to be brought forth from it.
It was narrated that Abu Sa‘eed al-Khudri (may Allah be pleased with him) said: The Messenger of Allah (blessings and peace of Allah be upon him) said: “Death will be brought in the form of a black and white ram, and a caller will call out: ‘O people of Paradise!’ They will crane their necks and look, and [the caller] will say: ‘Do you recognize this?’ They will say: ‘Yes, this is death.’ And all of them will have seen it. Then [the caller] will call out: ‘O people of Hell!’  They will crane their necks and look, and [the caller] will say: ‘Do you recognize this?’ They will say: ‘Yes, this is death.’ And all of them will have seen it. Then it will be slaughtered, then it will be said: ‘O people of Paradise, it is eternal and there will be no death. O people of Hell, it is eternal and there will be no death.’” Then he [the Prophet (blessings and peace of Allah be upon him)] recited the verse (interpretation of the meaning): “And warn them, [O Muhammad], of the Day of Regret, when the matter will be concluded; and [yet], they are in [a state of] heedlessness” – which is the heedlessness of the people of this world – “and they do not believe” [Maryam 19:39].
Narrated by al-Bukhaari (4453) and Muslim (2849).
According to a report of Ibn ‘Umar in al-Bukhaari (6182) and Muslim (2850): “When the people of Paradise go to Paradise and the people of Hell go to Hell, death will be brought and placed between Paradise and Hell. Then it will be slaughtered, and a caller will call out: ‘O people of Paradise, there is no death; O people of Hell, there is no death.’ Then the joy of the people of Paradise will increase, and the sorrow of the people of Hell will increase.”
See the words of Ibn al-Qayyim (may Allah have mercy on him), responding to someone who objected to this hadith on the basis of his reasoning, in the answer to question no. 10087.
Secondly:
With regard to the trial of the grave for those who committed major sins, there are three issues:

Answering the questions of the two angels, Munkar and Nakeer, with regard to belief, when they ask about his Lord, may He be glorified and exalted, about his religion, and about his Prophet (blessings and peace of Allah be upon him).
Punishment for his sins.
Will the evildoer be shown in his grave his place in Paradise?

With regard to the first matter, what appears to be the case is that people will be divided into two categories: Muslims and hypocrites or disbelievers. The Muslim will answer the questions of the two angels correctly, even if he was an evildoer; the disbeliever – or hypocrite – will not answer, and will be punished for that.
Ibn Hajar al-Haytami (may Allah have mercy on him) said:
What is implied by the hadiths that speak of the questioning of the two angels is that the believer, even if he was an evildoer, will answer them correctly,  but with regard to tidings he will receive, it is to be understood that it will be according to his status.
Al-Fataawa al-Hadeethiyyah (p. 7).
In the answer to question no. 21713, you will find the hadith of al-Baraa’ ibn ‘Aazib (may Allah be pleased with him) which speaks in detail of these two categories in the grave.
With regard to the second matter, the fact that the Muslim who was an evildoer will answer the questions of the two angels does not necessarily mean that he will not be punished for his committing of sins and disobedience, if he did not repent from them; in fact, in some cases the punishment of these people will continue until the onset of the Hour, and in other cases the punishment will cease.
Shaykh Muhammad as-Safaareeni (may Allah have mercy on him) said:
Whoever incurs the wrath and anger of Allah in this world, by committing acts that He has forbidden, and does not repent and dies in that state, he will suffer the punishment of al-barzakh commensurate with the level of divine wrath he has incurred, whether his sins were small or great, and whether he was a believer or disbeliever.
Lawaami‘ al-Anwaar al-Bahiyyah (2/18).
And he said:
Among those who will be punished in their graves, of whom the Prophet (blessings and peace of Allah be upon him) spoke are: tyrants, those who were arrogant; those who showed off; slanderers and backbiters; those who reviled the early generations (the salaf); those who went to soothsayers, astrologers and fortunetellers and asked them questions and believed them; and those who helped wrongdoers, selling their hereafter for the worldly benefit of others – and similar to them are those who were distracted by the sins and faults of others from dealing with their own sins and faults. All of these, and others like them, will be punished in their graves for these crimes, commensurate with their number and magnitude. Because most people are like that, the occupants of the graves will be punished, and those among them who are spared punishment will be few. Outwardly graves appear to be dust, but inwardly they are filled with regret and punishment. We ask Allah, may He be exalted, to grant us well-being, mercy, pardon and forgiveness, and Allah is the source of help [?].
Lawaami‘ al-Anwaar al-Bahiyyah (2/19).
In the answers to questions no. 45325 and 46068, you will find a detailed discussion of the causes of punishment in the grave.
With regard to the third matter, there are two possibilities:

the first is that the Muslim will be shown his place in Paradise on the grounds that he is not a disbeliever, and that Paradise is his ultimate destination, but this does not mean that he will not be punished in his grave, if it is Allah’s will that he be punished.

We are certain of the soundness of what our Prophet (blessings and peace of Allah be upon him) has told us, that there are some among the Muslims who will be punished in their graves until the Day of Resurrection, such as the one who had consumed riba, whom the Prophet (blessings and peace of Allah be upon him) saw swimming in a river of blood, and such as the adulterers, men and women, whom he (blessings and peace of Allah be upon him) saw screaming in an oven, and others. And we are certain that the ultimate destination of these people, if they were Muslims, will be Paradise.
It was narrated from Ibn ‘Umar (may Allah be pleased with him) that the Messenger of Allah (blessings and peace of Allah be upon him) said: “When one of you dies, he is shown his place morning and evening. If he is one of the people of Paradise, then (he is shown his place) among the people of Paradise, and if he is one of the people of Hell, then (he is shown his place) among the people of Hell. And it is said: ‘This is your place, until Allah, may He be glorified and exalted, resurrects you on the Day of Resurrection.’”
Narrated by al-Bukhaari (1379) and Muslim (2866).
Ibn Hajar (may Allah have mercy on him) said:
Al-Qurtubi (may Allah have mercy on him) said: With regard to the believer and the disbeliever, this is clear. With regard to the believer whose  deeds were mixed, it may apply to him also, because he will enter Paradise as all believers will ultimately do.
Fath al-Baari (3/243).
Shaykh Abu’l-Hasan ‘Ubaydullah ibn al-‘Allaamah Muhammad ‘Abd as-Salaam al-Mubararakfoori said:
The showing of the two places [in either Paradise or Hell] will happen to the sincere believer, the disbeliever, and the believer whose deeds were mixed, because the latter will enter Paradise as all believers will ultimately do. He will be shown his place in Paradise, and it will be said to him: This is your place, and you will go to it after you have received the punishment that you deserve.
Mirqaat al-Mafaateeh Sharh Mishkaat al-Masaabeeh (1/222).

The second is that it may be said that the place in Paradise may be shown to the believer whose deeds were mixed or the Muslim who was an evildoer by way of telling him: this would have been your place in your grave if you had not sinned and thus deserved punishment, and his place in Hell may be shown to him and it may be said to him: This is because of your sins.

Al-Haafiz Ibn Hajar (may Allah have mercy on him) said:
Based on that, it may be that in the case of the sinner for whom it is decreed that he is to be punished before he is admitted to Paradise, it will be said to him, for example, after he is shown his place in Paradise: This would have been your place from the outset if you had not sinned, and this is your place from the outset because of your sin.
We ask Allah to pardon us and save us from every trial in this life and after death, for He is the Possessor of immense grace.
Fath al-Baari (11/366).
Allah knows best what is the case in this matter. We ask Allah to make us and you among those on the right, and to help us to remember Him, give thanks to Him and worship Him properly.