Ubayy b. Ka‘b said:

God’s messenger asked, “Abul Mundhir (this is Ubayy’s Kunya), do you know which verse of God’s Book that you have is greatest?” I replied, “God and His messenger know best.” He repeated his question and I said, “God, there is no god but He, the Living, the Eternal.” Thereupon he struck me on the breast and said, “May knowledge be pleasant for you, Abul Mundhir!” Muslim transmitted it.

وَعَنْ أُبَيِّ بْنِ كَعْبٍ قَالَ: قَالَ رَسُولُ اللَّهِ صَلَّى اللَّهُ عَلَيْهِ وَسَلَّمَ: «يَا أَبَا الْمُنْذِرِ أَتَدْرِي أَيُّ آيَةٍ مِنْ كِتَابِ اللَّهِ مَعَك أعظم؟» . قَالَ: قُلْتُ اللَّهُ وَرَسُولُهُ أَعْلَمُ قَالَ: «يَا أَبَا الْمُنْذِرِ أَتَدْرِي أَيُّ آيَةٍ مِنْ كِتَابِ اللَّهِ مَعَك أعظم؟» . قَالَ: قُلْتُ (اللَّهُ لَا إِلَهَ إِلَّا هُوَ الْحَيُّ القيوم) قَالَ فَضرب فِي صَدْرِي وَقَالَ: «وَالله لِيَهنك الْعلم أَبَا الْمُنْذر» . رَوَاهُ مُسلم