Reported by Ubayy bin Ka`b (RA): The Messenger of Allah (peace be upon him) said: "Abu Mundhir! Do you know which Ayah in Allah's Book is the greatest?'' I replied: "It is `Allah la ilaha illa Huwal-Haiyul-Qayum (Allah! none has the right to be worshipped but He, the Ever Living...)'.'' (2:256) Thereupon he (peace be upon him) patted me in the chest and said, "Rejoice by this knowledge, O Abu Mundhir!'' [Muslim].