Sahih Bukhari Volume 6, Book 66, Hadith 5012

وَقَالَ عُثْمَانُ بْنُ الْهَيْثَمِ حَدَّثَنَا عَوْفٌ، عَنْ مُحَمَّدِ بْنِ سِيرِينَ، عَنْ أَبِي هُرَيْرَةَ ـ رضى الله عنه ـ قَالَ وَكَّلَنِي رَسُولُ اللَّهِ صلى الله عليه وسلم بِحِفْظِ زَكَاةِ رَمَضَانَ فَأَتَانِي آتٍ فَجَعَلَ يَحْثُو مِنَ الطَّعَامِ فَأَخَذْتُهُ فَقُلْتُ لأَرْفَعَنَّكَ إِلَى رَسُولِ اللَّهِ صلى الله عليه وسلم فَقَصَّ الْحَدِيثَ فَقَالَ إِذَا أَوَيْتَ إِلَى فِرَاشِكَ فَاقْرَأْ آيَةَ الْكُرْسِيِّ لَنْ يَزَالَ مَعَكَ مِنَ اللَّهِ حَافِظٌ وَلاَ يَقْرَبُكَ شَيْطَانٌ حَتَّى تُصْبِحَ‏.‏ وَقَالَ النَّبِيُّ صلى الله عليه وسلم ‏"‏ صَدَقَكَ وَهْوَ كَذُوبٌ ذَاكَ شَيْطَانٌ ‏"‏‏.

Narrated Abu Huraira: Allah 's Apostle ordered me to guard the Zakat revenue of Ramadan. Then somebody came to me and started stealing of the foodstuff. I caught him and said, "I will take you to Allah's Apostle!" Then Abu Huraira described the whole narration and said:) That person said (to me), "(Please don't take me to Allah's Apostle and I will tell you a few words by which Allah will benefit you.) When you go to your bed, recite Ayat-al-Kursi, (2.255) for then there will be a guard from Allah who will protect you all night long, and Satan will not be able to come near you till dawn." (When the Prophet heard the story) he said (to me), "He (who came to you at night) told you the truth although he is a liar; and it was Satan."