Sahih Bukhari Volume 5, Book 57, Hadith Number 10.

Narated By ‘Abdullah bin Abi Mulaika : The people of Kufa sent a letter to Ibn Az-Zubair, asking about (the inheritance of) (paternal) grandfather. He replied that the right of the inheritance of (paternal) grandfather is the same as that of father if the father is dead) and added, “Allah’s Apostle said, ‘ If I were to take a Khalil from this nation, I would have taken him (i.e. Abu Bakr).”