Short answer
The Prophet ﷺ said a surah of thirty ayat interceded for a man until he was forgiven, and that it is Surah al-Mulk (Tabarak). Companions such as Ibn Mas'ud called it the protector from the punishment of the grave. Reciting it every night, usually before sleeping, is a recommended practice.
Reciting Surah al-Mulk every night is mustahabb. It may be recited from memory, from a mushaf with wudu, or on a screen, and lying in bed is allowed.
The four schools agree on this.
Explanation
Intercession: Abu Hurayrah reported that the Prophet ﷺ said: "There is a surah of the Quran of thirty ayat that interceded for a man until he was forgiven: Tabarak alladhi biyadihil mulk" (Abu Dawud, al-Tirmidhi, graded hasan). Al-Mulk is the 67th surah and has exactly thirty ayat.
Protection in the grave: Ibn Mas'ud said that whoever recites Tabarak every night, Allah protects him by it from the punishment of the grave, and that in the time of the Prophet ﷺ they called it al-mani'ah, the protector. This is reported by al-Nasa'i in his larger collection. A similar report in al-Tirmidhi calls it "the protector and the saviour", but its chain is weak.
How people keep it:
- Recite it after Isha or in bed before sleeping. Many learn it by heart for this reason; it takes about five to ten minutes.
- Pair it with Surah al-Sajdah, which the Prophet ﷺ is also reported to have recited at night, and with the last three surahs.
- Reading it from a phone is fine: see reading lying down.
The surah itself is a reflection on Allah's power over life and death, the heavens and the earth, and the reckoning (67:1 to 2). Reading it with its meaning makes the habit stronger. Read it at Surah al-Mulk.
The evidence
Quran, Surah Al-Mulk 67:1-2
بِسْمِ ٱللَّهِ ٱلرَّحْمَٰنِ ٱلرَّحِيمِ تَبَٰرَكَ ٱلَّذِى بِيَدِهِ ٱلْمُلْكُ وَهُوَ عَلَىٰ كُلِّ شَىْءٍۢ قَدِيرٌ ﴿١﴾ ٱلَّذِى خَلَقَ ٱلْمَوْتَ وَٱلْحَيَوٰةَ لِيَبْلُوَكُمْ أَيُّكُمْ أَحْسَنُ عَمَلًۭا ۚ وَهُوَ ٱلْعَزِيزُ ٱلْغَفُورُ ﴿٢﴾
Blessed is He in whose hand is dominion, and He is over all things competent - [He] who created death and life to test you [as to] which of you is best in deed - and He is the Exalted in Might, the Forgiving -
The opening of Surah al-Mulk on Allah's dominion over life and death.
Jami' at-Tirmidhi 2891
Grading to be checked... إن سورة من القرآن ثلاثون آية شفعت لرجل حتى غفر له ...
"A surah of the Quran of thirty ayat interceded for a man until he was forgiven: Tabarak alladhi biyadihil mulk."
The intercession of Surah al-Mulk.
Sunan Abi Dawud 1400
Grading to be checked... إن سورة من القرآن ثلاثون آية تشفع لصاحبها حتى يغفر له ...
"A surah of the Quran of thirty ayat will intercede for its companion until he is forgiven."
The same virtue in Abu Dawud's wording.
Checked by our team. For a more accurate answer to your own situation, consult a scholar. Quran translation by Sahih International. Hadith Arabic from the standard editions of the six books and the Muwatta, with gradings as recorded there; the English is our own rendering. Spotted a mistake? Tell us.