Sayyiduna Abdullah (bin Mas'ud) (may Allah be pleased with him) says: "By the One besides whom there is no god, no surah of the Qur'an was revealed except that I know where it was revealed, and no verse (was revealed) except that I know concerning whom it was revealed; and if I knew of anyone more knowledgeable than me about the Book of Allah, whom camels could reach, I would ride to him."
Hadith Referenceالمعجم الكبير للطبراني / باب العين / 8398