O Abu al-Mundhir, do you know which verse of Allah's Book that you have is the greatest?" I said: "{Allah: none has the right to be worshiped except Him, the Ever-Living, All-Sustaining...} [Surat al-Baqarah: 255]." Thereupon, he struck me on the chest and said: "May knowledge be pleasant for you, O Abu al-Mundhir!

The Prophet (may Allah's peace and blessings be upon him) asked Ubayy ibn Ka‘b about the greatest verse in Allah's Book. He initially hesitated about the answer and then said: {Allah: none has the right to be worshiped except Him, the Ever-Living, All-Sustaining...} The Prophet (may Allah's peace and blessings be upon him) agreed with him and struck him on the chest, indicating that it is filled with knowledge and wisdom. He also supplicated that this knowledge be pleasant and easy for him.