Surah Al-Baqarah (2)
is the correct answer.
This is Ayah 255 of Surah Al-Baqarah.
This is Ayat Al-Kursi and tremendous virtues have been associated with it, for the authentic Hadith describes it as `the greatest Ayah in the Book of Allah.' Imam Ahmad recorded that `Ubayy bin Ka`b
said that the Prophet
asked him about the greatest Ayah in the Book of Allah, and `Ubayy
answered, "Allah and His Messenger know better.'' When the Prophet
repeated his question several times, `Ubayy
said, "Ayat Al-Kursi.'' The Prophet
“Congratulations for having knowledge, O Abu Al-Mundhir! By He in Whose Hand is my soul! This Ayah has a tongue and two lips with which she praises the King (Allah) next to the leg of the Throne.”
This Hadith was also collected by Muslim, but he did not include the part that starts with, "By He in Whose Hand...''
Excerpt : Tafsir ibn Kathir Abridged English Version