Hadithcore
Riyad as-Salihin, 1019

Ubayy bin Ka'b (May Allah be pleased with him) reported:

The Messenger of Allah (ﷺ) 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 (ﷺ) patted me in the chest and said, "Rejoice by this knowledge, O Abu Mundhir!" <b>[Muslim]</b>.

وعن أبي بن كعب رضي الله عنه قال‏:‏ قال رسول الله صلى الله عليه وسلم ‏:‏‏"‏ يا أبا المنذر أتدري أي آية من كتاب الله معك أعظم ‏؟‏ قلت‏:‏ الله لا إله إلا هو الحي القيوم، فضرب في صدري وقال ‏:‏‏"‏ ليهنك العلم أبا المنذر‏"‏‏.‏ ‏(‏‏(‏رواه مسلم ‏)‏‏)‏‏.‏

References1 variant
In-Book Reference
Book 8, Hadith 29
Sharh · explanationclick to expand
<b>Guidance from the Hadith:</b><br> 1) The verse of Al-Kursi is the greatest verse in the Book of Allah, for it comprises sublime meanings involving the oneness of Allah and His excellent names and attributes.<br> 2) The verse of Al-Kursi contains ten phrases about the attributes of Allah Almighty, all of which manifest sincere belief in the oneness of Allah Almighty.<br> 3) Knowing the oneness of Allah is the great knowledge that is a cause for joy and bliss.
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