Abu Hurairah (radi Allahu anhu) said: "The Messenger of Allah (sal Allahu alaihi wa sallam) deputised me to keep (guard over) Sadaqah of Ramadan. Someone came and started taking handfuls of the Sadaqah quickly. I took hold of him and said, 'By Allah, I will take you to the Messenger of Allah.' He said, 'I am needy and have many dependents.' I released him, and in the morning the Messenger of Allah (sal Allahu alaihi wa sallam) asked me, 'What did your prisoner do yesterday?' I said, 'O Messenger of Allah! The person complained of being needy and of having many dependents, so I pitied him and let him go.' The Messenger of Allah (sal Allahu alaihi wa sallam) said, 'Indeed, he told you a lie and he will return.' I believed that he would return again as the Messenger of Allah (sal Allahu alaihi wa sallam) had told me that he would return. So I waited for him watchfully. When he returned and started stealing handfuls of foodstuff I caught hold of him again and said, 'I will definitely take you to the Messenger of Allah.' He said, 'Leave me, for I am very needy and have many dependents. I promise I will not come back again.' I pitied him and let him go.

In the morning the Messenger of Allah (sal Allahu alaihi wa sallam) asked me, 'What did your prisoner do?' I replied, 'O Messenger of Allah! He complained of his great need and of too many dependents, so I took pity on him and set him free.' The Messenger of Allah (sal Allahu alaihi wa sallam) said, 'Verily, he told you a lie and he will return.' I waited for him attentively for the third time, and when he came and started stealing handfuls of the Sadaqah, I caught hold of him and said, 'I will surely take you to the Messenger of Allah as it is the third time you promise not to return, yet you break your promise and come.' He said, 'Forgive me and I will teach you some words with which Allah will benefit you.' I asked, 'What are they?' He replied, 'When ever you go to bed, recite Ayat al-Kursi: 'Allah – There is no God but He, the Living, the Everlasting', till you finish the whole verse. If you do so, Allah will appoint a guard for you who will stay with you and no devil will come near you till morning.' So, I released him.

In the morning, the Messenger of Allah (sal Allahu alaihi wa sallam) asked, 'What did your prisoner do yesterday?' I replied, 'He claimed that he would teach me some words by which Allah will benefit me, so I let him go.' The Messenger of Allah (sal Allahu alaihi wa sallam) asked, 'What are they?' I replied, 'He said to me, ‘When ever you go to bed, recite Ayat al-Kursi from the beginning to the end: ‘Allah – There is no God but He, the Living, the Everlasting.’ He further said to me, ‘If you do so, Allah will appoint a guard for you, who will stay with you, and no devil will come near you till morning.’ The Prophet (sal Allahu alaihi wa sallam) said, 'He really spoke the truth, although he is an absolute liar. Do you know whom you were talking to, these three nights, O Abu Hurairah?' Abu Hurairah said, 'No.' He said, 'It was Shaytan (the Devil).'" [Sahih Bukhari: Book of Wakalah]