Sayyiduna Abdullah bin Mas'ud (may Allah be pleased with him) said: A man is approached in his grave (for punishment). He is approached from the side of his legs, and they say: 'You have no way through us; he used to recite Surah al-Mulk upon us.' Then he is approached at his belly, and it says: 'You have no way over me; he kept Surah al-Mulk preserved within me.' Then he is approached from the side of his head, and it says: 'You have no way through me; he used to recite Surah al-Mulk with me.' Sayyiduna Abdullah (may Allah be pleased with him) said: "This is al-Mani'ah (the Protector); it prevents the punishment of the grave. In the Torah it is this Surah al-Mulk; whoever recites it in a night has done much and done well."
Hadith Referenceالمعجم الكبير للطبراني / باب العين / 8619