Narrated Abu Huraira (Radi Allahu Anhu): Prophet Muhammad (salallahu alaihi wasallam) 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 Ayatul 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.”
Sahih Al-Bukhari – Book 61 Hadith 530.