Sahih Bukhari Volume 4, Book 56, Hadith Number 821.

Narated By Said bin Jubair : About Ibn ‘Abbas: ‘Umar bin Al-Khattab used to treat Ibn ‘Abbas very favorably ‘Abdur Rahman bin ‘Auf said to him. “We also have sons that are equal to him (but you are partial to him.)” Umar said, “It is because of his knowledge.” Then ‘Umar asked Ibn ‘Abbas about the interpretation of the Verse:- ‘When come the Help of Allah and the conquest (of Mecca) (110.1) Ibn ‘Abbas said. “It portended the death of Allah’s Apostle, which Allah had informed him of.” ‘Umar said, “I do not know from this Verse but what you know.”