Sahih Bukhari Volume 6, Book 61, Hadith Number 522.

Narrated By Shaqiq bin Salama : Once ‘Abdullah bin Mas’ud delivered a sermon before us and said, “By Allah, I learnt over seventy Suras direct from Allah’s Apostle. By Allah, the companions of the Prophet came to know that I am one of those who know Allah’s Book best of all of them, yet I am not the best of them.” Shaqiq added: I sat in his religious gathering and I did not hear anybody opposing him (in his speech).