Can you tell me about Hizb al- Tahreer? I heard that they do not believe in torment of grave? is it correct? Is it permissible to add or deduct something from Shariah?

Praise be to Allah, the Lord of the Worlds; and blessings and peace be upon our Prophet Muhammad and upon all his Family and Companions.
1. We do not have the books of this group to confirm the matter you mentioned. But Professor Abdur Rahman Dimishqiyah quoted in his book named (Hizb al-Tehreer: a scientific discussion about the basics of the Hizb and a scientific falsification to their claims about 'al-Khaber al-Wahid' -single narration-) from Umar Bakri Fustuqi, the Mufti of this group, that he said: "I urge you to believe in the torment of the grave, in the coming of Mahdi, but whoever believes in these matters commits a sin".
This is a clear contradiction and an open violation to the beliefs of Ahl al-Sunnah. How can a person become a wrong doer for believing in the torment of the grave? Then what is the meaning of 'I urge you to believe in it'?
Many Muslim scholars reported the consensus of Ahlu-al-Sunnah that the torment of the grave is true. Among them are Abul Hasan al-Ashari, al-Qurtubi, Ibn Taymiyah and others.
Imam al-Baghdadi wrote in his book "al-Farq Bayna al-Firaq". 'Muslims have agreed that the torment of the grave is true and whoever denies it will be punished in his grave, because he deviated from the Muslim Ummah, and whoever sets himself apart from it will be set apart in Hell Fire.'
The sources for the matters of faith are Qur'an, Hadith, Consensus of Companions of Prophet Muhammad (Blessings and peace of Allah be upon them) and their immediate followers and those who follow them. No one has the right to add to it or deduct from it.
For more details, you may refer to the book of Professor Dimeshqiyah, mentioned above, and the simplified encyclopedia of religions and modern sects. Published by WAMY, Riyadh, K.S.A.
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Allah knows best.