Silsilat al-Ahadith al-Sahihah

It is narrated from Sayyiduna Ubayy bin Ka'b (may Allah be pleased with him) that the Noble Prophet (peace and blessings be upon him) said: "Which verse in the Book of Allah is the greatest?" He replied: Allah and His Messenger know best. But the Prophet (peace and blessings be upon him) repeated the question several times. (Eventually) Sayyiduna Ubayy (may Allah be pleased with him) said: It is Ayat al-Kursi. The Noble Prophet (peace and blessings be upon him) said: "Abu'l-Mundhir! May this knowledge be blessed for you. By Him in Whose hand is my soul! This verse has a tongue and two lips; it glorifies (Allah) at the foot of the Throne."