All perfect praise be to Allaah, The Lord of the Worlds. I testify that there is none worthy of worship except Allaah, and that Muhammad is His slave and Messenger. We ask Allaah to exalt his mention as well as that of his family and all his companions.
We will start our answer with the authentic narration, which is the third narration, but has a different wording. Abu Hurayrah narrated his story with the devil who used to take handfuls of the foodstuff (of the Zakat) (stealthily), in a long narration. The narration reads: "…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 Allaah's Apostle as it is the third time you promise not to return, yet you broke your promise and came back." He said: "(Forgive me and) I will teach you some words with which Allaah will benefit you." I asked: "What are they?" He replied: "Whenever you go to bed, recite "Ayatul-Kursi" [Quran 2:255] 'Allaahu laa ilaaha illa huwa-l-Hayy-ul Qayyum' till you finish the whole verse. (If you do so), Allaah will appoint a guard for you who will stay with you and no devil will come near you till the morning." So, I released him.
In the morning, the Prophet asked: "What did your prisoner do yesterday?" I replied: "He claimed that he would teach me some words by which Allaah will benefit me, so I let him go." Allaah's Apostle asked: "What were they?" I replied: "He said to me, 'Whenever you go to bed, recite Ayatul-Kursi from the beginning to the end, 'Allaahu laa ilaaha illa huwa-l-Hayy-ul Qayyum.' He further said to me: '(If you do so), Allaah will appoint a guard for you who will stay with you, and no devil will come near you till morning.' [Abu Hurayrah 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 with whom you were talking these three nights, O Abu Hurayrah?" He said, "No." He said, "It was the devil." [Al-Bukhari]
As regards the remaining narrations, we have not come across any of them despite our great effort and long search in trying to find them. It appears that these narrations are not authentic from the Prophet . However, we came across one narration which is nearly similar to the narration which you mentioned. The narration reads: "Whoever reads "Ayatul-Kursi" [Quran 2:255], when he finishes his ablution, Allaah will give him the reward of forty years of worship, and increases him forty degrees, and marries him with forty women of
The other narration we come across reads: "The master of the Quran is chapter two, and the master of chapter two is "Ayatul-Kursi" [Quran 2:255], which contains five words [phrases], each of which contains fifty blessings." Al-Albaani said: 'This narration is fabricated.'
For more benefit, we will mention other authentic narrations which are reported about the excellence of reciting "Ayatul-Kursi" [Quran 2:255], in addition to the narration reported by Abu Hurayrah which we already mentioned, and this will suffice you from using the weak narrations.
Ubay Ibn Ka'b narrated that the Prophet asked: "O Abul-Munthir, which is the greatest verse in the Quran? I replied: "Allaah and His Messenger know best." He again asked the same question. I replied: "Allaahu Laa Ilaaha Illa Huwwal-Hayyul-Qayyoom" "Allaah, none has the right to be worshipped but Him, the Ever-Living, the One Who sustains and protects all that exists." [Quran 2:255]. He [Abul-Munthir] said: ''Then he kindly hit me on my chest and said: "Congratulations to you for your knowledge, O Abul-Munthir." [Muslim]
Furthermore, Abu Umaamah narrated that the Prophet said: "Whoever reads "Ayatul-Kursi" [Quran 2:255], after every obligatory prayer, nothing prevents him from entering
Allaah Knows best.