Ayatul-Kursi and Confirming Proofs of at-Tawheed
Imam Muslim collected a hadith in his Saheeh on the the authority ob Ubay bin Ka’b (radhiallahu ‘anhu) that he said
“Allah’s Messenger (sallallahu ‘alayhi wa sallam) said, ‘O Abul-Mundhir! Do you know which verse from the book of Allah is the greatest? Ubay bin Ka’b said, “I replied, ‘Allah and His Messenger know best’. The Prophet (sallallahu ‘alayhi wa sallam) said, ‘O Abul-Mundhir! Do you know which verse from the book of Allah is the greatest? Ubay bin Ka’b said, “I said, “Allah! Lâ ilâha illa Huwa (none has the right to be worshipped but He), the Ever Living, the One Who sustains and protects all that exists.” Ubay bin Ka’b said, “He smacked my chest and said, “By Allah! Congratulations, Abul-Mundhir for having knowledge.”
Meaning congratulations for this knowledge which Allah has gifted you, facilitated for you, and has blessed you with. The Prophet (sallallahu ‘alayhi wa sallam) swore by Allah exalting this status and emphasizing this ambition.
Among Ubay’s excellent perception and keenness (radhiallahu ‘anhu) is that when the Prophet (sallallahu ‘alayhi wa sallam) questioned him he continued in his search for the verse which is dedicated to clarifying the greatest matter in the Quran, At-Tawheed, an acknowledgement of its confirming proofs, and a mention of Allah’s greatness and perfection which He is deserving solely to be worshipped. This was from the completeness of his understanding and excellent understanding of the religion.
He didn’t cite a verse clarifying praiseworthy etiquettes, subsidiary judgments, past events, horrors of the Day of resurrection or similar to that; rather, ’Ubay selected the verse which is dedicated to clarifying and acknowledging at-Tawheed.