It has been told in Hadith that Prophet Muhammad (salallahu alayhi wa sallam) has said that if every night Surat ul-Mulk is recited, then the reciter shall be protected from the tortures of the grave.
The Prophet (salallahu alayhi wa sallam) said, 'There is a surah in the Qur'an which is only thirty verses. It defended whoever recited it until it puts him into paradise' i.e. Surah al-Mulk
[Fath al Qadir 5/257, Sahihul Jamiea 1/680, Tabrani in Al-Awsat & Ibn Mardawaith]
The Prophet (salallahu alayhi wa sallam) said, 'Surah al-Mulk is the protector from the torment of the grave'
[Sahihul Jamiea 1/680, Hakim 2/498 & Nasai]
Jabir (radiyallahu anhu) said it was the custom of the Prophet (salallahu alayhi wa sallam) not to go to sleep until he had read Tabarakalladhi Biyadihil Mulk and Alif Laam Meem Tanzeel. [Ahmad, Tirmidhi and Darami]
Anas (radiyallahu anhu) reported Rasulullah (sallallahu alaiyhi wa sallam) as saying, "There is a Surah which will plead for its reciter till it causes him to enter paradise (Tabarakallahi Biyadihil Mulk)." [at-Tabrani]
Abdullah bin 'Abbas (radiyallahu anhuma) reported that the Prophet (salallahu alayhi wa sallam)said, 'It is my desire/love that Surah al-Mulk should be in the heart of every Muslim' [Hakim, al-Hisnul Haseen by the cassical scholar Muhammad al-Jazri]
Ibn Abbas (radiyallahu anhuma) said that one of the companions of the Prophet (salallahu alayhi wa sallam) set up his tent over a grave without realising that it was a grave and it contained a man who was reciting the Surah Tabarakalladhi Biyadihil Mulk up to the end. He went and told the Prophet (salallahu alayhi wa sallam) who said, 'It is The Defender; it is The Protector which safeguards from the punishment of Allah Ta'ala [at-Tirmidhi]