Abu Hurairah (May Allah be pleased with him) reported

The Messenger of Allah (ﷺ) put me in charge of charity of Ramadan (Sadaqat-ul- Fitr). Somebody came to me and began to take away some food-stuff. I caught him and said, "I must take you to the Messenger of Allah (ﷺ)." He said, "I am a needy man with a large family, and so I have a pressing need." I let him go. When I saw the Messenger of Allah (ﷺ) next morning, he asked me, "O Abu Hurairah! What did your captive do last night?" I said, "O Messenger of Allah! He complained of a pressing need and a big family. I felt pity for him so I let him go." He (ﷺ) said, "He told you a lie and he will return." I was sure, according to the saying of the Messenger of Allah (ﷺ) that he would return. I waited for him. He sneaked up again and began to steal food-stuff from the Sadaqah. I caught him and said; "I must take you to the Messenger of Allah (ﷺ)." He said, "Let go of me, I am a needy man. I have to bear the expenses of a big family. I will not come back." So I took pity on him and let him go. I went at dawn to the Messenger of Allah (ﷺ) who asked me, "O Abu Hurairah! What did your captive do last night?" I replied, "O Messenger of Allah! He complained of a pressing want and the burden of a big family. I took pity on him and so I let him go." He (ﷺ) said, "He told you a lie and he will return." (That man) came again to steal the food-stuff. I arrested him and said, "I must take you to the Messenger of Allah (ﷺ), and this is the last of three times. You promised that you would not come again but you did." He said, "Let go of me, I shall teach you some words with which Allah may benefit you." I asked, "What are those words?" He replied, "When you go to bed, recite Ayat-ul- Kursi (2:255) for there will be a guardian appointed over you from Allah, and Satan will not be able to approach you till morning." So I let him go. Next morning the Messenger of Allah (ﷺ) asked me, "What did your prisoner do last night." I answered, "He promised to teach me some words which he claimed will benefit me before Allah. So I let him go." The Messenger of Allah (ﷺ) asked, "What are those words that he taught you?" I said, "He told me: 'When you go to bed, recite Ayat- ul-Kursi from the beginning to the end i.e.,[ Allah! none has the right to be worshipped but He, the Ever Living, the One Who sustains and protects all that exists. Neither slumber nor sleep overtakes Him. To Him belongs whatever is in the heavens and whatever is on the earth. Who is he that can intercede with Him except with His Permission? He knows what happens to them (His creatures) in this world, and what will happen to them in the Hereafter. And they will never compass anything of His Knowledge except that which He wills. His Kursi encompasses the heavens and the earth, and preserving them does not fatigue Him. And He is the Most High, the Most Great].' (2:255). He added: 'By reciting it, there will be a guardian appointed over you from Allah who will protect you during the night, and Satan will not be able to come near you until morning'." The Messenger of Allah (ﷺ) said, "Verily, he has told you the truth though he is a liar. O Abu Hurairah! Do you know with whom you were speaking for the last three nights?" I said, "No." He (ﷺ) said, "He was Shaitan (Satan)."

[Al-Bukhari].