The Best Ayah in the Noble Qur'an
Allah – there is no deity except Him, the Ever-Living, the Sustainer of [all] existence. Neither drowsiness overtakes Him nor sleep. To Him belongs whatever is in the heavens and whatever is on the earth. Who is it that can intercede with Him except by His permission? He knows what is [presently] before them and what will be after them, and they encompass not a thing of His knowledge except for what He wills. His Kursī extends over the heavens and the earth, and their preservation tires Him not. And He is the Most High, the Most Great.
(2:255)
Note: Ubayy bin Ka'b (radiAllahu anhu) reported: The Messenger of Allah (peace be upon him) said:
"Abu Mundhir! Do you know which Ayah in Allah's Book is the greatest? I said: 'Allah and His messenger know best.'
He (peace be upon him) again said:
'Do you know which Ayah in Allah's Book, according to you, is the greatest?' I (Abu Mundhir) replied:
‘It is 'Allah la ilaha illa Huwal-Hayyul-Qayyum'.[2:255].
Thereupon he (peace be upon him) patted me in the chest and said,
' Rejoice by your knowledge, O Abu Mundhir! (i.e, may this knowledge be a source of respect, honour and benefit to you)'."
[Muslim]