The Messenger of Allah ﷺ said, "Abu Mundhir, do you know which verse from the Book of Allah that you have memorized is the greatest?"I replied, "Allah and His Messenger know best."He said again, "Abu Mundhir, do you know which verse from the Book of Allah that you have memorized is the greatest?"I answered, "Allah, there is no god but He, the Living, the Sustainer" [Baqarah 2:255].He struck me on the chest and said, "By Allah, may this knowledge bring you joy, Abu Mundhir."
قال رسول الله ﷺ: يا أبا المنذر أتدري أي آية من كتاب الله معك أعظم؟ قال: قلت: الله ورسوله أعلم، قال: يا أبا المنذر أتدري أي آية من كتاب الله معك أعظم؟ قال: قلت: {الله لا إله إلا هو الحي القيوم} قال: فضرب صدري وقال: والله ليهنك العلم أبا المنذر.
Muslim narrated it in Fadail Quran (810:258), from Abu Bakr bin Abu Shayba, who said, Abdul-Ala bin Abdul-Ala related it to us, from Jareeri, from Abu Saleel, from Abdullah bin Rabah Ansari, from Ubayy bin Kaab, and he mentioned it.Abdul-Razzaq narrated it in his Musannaf (6001), and from him Imam Ahmad (21278), from Sufyan Thawri, from Saeed Jariri, from Abu Saleel, from Abdullah bin Rabah, from Ubayy bin Kaab, with similar wording, and he added in it, "By the One in whose hand is my soul, it has a tongue and two lips, which glorify the King at the foot of the Throne." Its isnad is sahih.