A Scholar of the Holy Qur’an
Hazrat Ubayy bin Kaab was well versed in the Holy Quran. On one occasion, the Holy Prophet (sa) asked him – and I have narrated this incident in a previous sermon, two or three weeks ago – (he asked) “Which verse of the Quran should be declared the greatest verse?” Initially he replied by saying, “God and His Messenger (sa) know best.” When the Holy Prophet (sa) insisted, he said “Ayatul Kursi could be declared the greatest verse.” I also related an incident regarding Ayatul Kursi. The Holy Prophet (sa) was pleased to hear this and said, “O Ubayy! May Allah bless your level of knowledge. Undoubtedly Ayatul Kursi is a great verse of the Quran.”
(Sunan Abi Dawood, Kitab Al-Witr, Bab Ma Ja’a Fi Ayatil Kursi, Hadith 1460)
In another narration, it is mentioned that the same year the Holy Prophet (sa) passed away, he completed one reading of the Holy Quran with Ubayy bin Kaab.
(Kanzul Ummal, Vol. 13 p. 266, Hadith 36779, Beirut 1985)
With the permission of Hazrat Umar (ra), [Ubayy bin Kaab] would teach people the knowledge of the Quran as well as its exegesis.
(Sahih Al-Bukhari, Salat Al-Tarawih, Hadith 2010)