‘Abdullaah ibn Mas’ood (radhiAllahu ‘anhu) said:
“Whoever reads ‘al-Mulk’ every night, Allaah will protect him from the torment of the grave. At the time of the Messenger of Allaah (sallAllahu ‘alayhi wa sallam), we used to call it al-mani’ah (that which protects). In the Book of Allah, there is a chapter [and] whoever recites it every night has done very well.”
[Sahih at-Targhib wat-Tarhib, no. 1475]
Imam Ahmad recorded from Abu Hurayrah (may Allah be pleased with him) that Allah’s Messenger (sallAllahu ‘alayhi wa sallam) said,
“Verily, there is a chapter in the Qur’an which contains thirty Ayat that will intercede on behalf of its reciter until he is forgiven. (It is): ‘Blessed be He in Whose Hand is the dominion.’”
[This Hadith was collected by At-Tirmidhi and the four Sunan Compilers. At-Tirmidhi said concerning it, “This is a Hasan Hadith.”]
He (sallAllahu ‘alayhi wa sallam) used to recite Surah As-Sajdah and Surah Al-Mulk (in Arabic) before sleeping.
[Reference: At-Tirmithi, An-Nasa’i. See also Al-Albani, Sahihul-Jami ’ As-Saghir 4/255]
Abu Hurairah (may Allah be pleased with him) reported: I heard the Messenger of Allah (sallAllahu ‘alayhi wasallam) saying,
“There is a Surah in the Qur’an which contains thirty Ayat which kept interceding for a man until his sins are forgiven. This Surah is ‘Blessed is He in Whose Hand is the dominion.’ (Surat Al-Mulk 67).”
[At-Tirmidhi and Abu Dawud]
Commentary from Riyad-us-Saliheen:
This Hadith means that on the Day of Resurrection this Surah will intercede with Allaah for the forgiveness of its reciter. This Hadith has been narrated (in Arabic) in the past tense because, like the past indefinite, its occurrence is definite and not open to inquiry. At some places, however, it has also been narrated in the present tense.