What miracle did the Prophet Muhammad (peace be upon him) tell Abu Huraira about so that Abu Huraira was able to ward off Satan?
      Narrated Abu Huraira:                          Allah's Apostle deputed me to keep Sadaqat (al-Fitr) of Ramadan. A      comer came and started taking handfuls of the foodstuff (of the      Sadaqa) (stealthily). I took hold of him and said, "By Allah, I will      take you to Allah's Apostle ." He said, "I am needy and have many      dependents, and I am in great need." I released him, and in the      morning Allah's Apostle asked me, "What did your prisoner do      yesterday?" I said, "O Allah's Apostle! The person complained of being     needy and of having many dependents, so, I pitied him and let him go."     Allah's Apostle said, "Indeed, he told you a lie and he will be coming     again." I believed that he would show up again as Allah's Apostle had      told me that he would return. So, I waited for him watchfully. When he     (showed up and) started stealing handfuls of foodstuff, I caught hold      of him again and said, "I will definitely take you to Allah's Apostle.     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 Allah's Apostle asked me, "What did your prisoner do."      I replied, "O Allah's Apostle! He complained of his great need and of      too many dependents, so I took pity on him and set him free." Allah's      Apostle 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 foodstuff, I caught hold of him and said, "I      will surely take you to Allah's Apostle 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, "Whenever you go      to bed, recite "Ayat-al-Kursi"-- 'Allahu la ilaha illa huwa-l-Haiy-ul      Qaiyum' till you finish the whole verse. (If you do so), Allah will      appoint a guard for you who will stay with you and no satan will come      near you till morning. " So, I released him. In the morning, Allah's      Apostle 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." Allah's Apostle asked, "What are they?" I      replied, "He said to me, 'Whenever you go to bed, recite Ayat-al-Kursi     from the beginning to the end ---- Allahu la ilaha illa      huwa-lHaiy-ul-Qaiyum----.' He further said to me, '(If you do so),      Allah will appoint a guard for you who will stay with you, and no      satan will come near you till morning.' (Abu Huraira or another      sub-narrator) added that they (the companions) were very keen to do      good deeds. The Prophet 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 Huraira?" Abu Huraira said, "No." He said, "It was      Satan."