Abu Dawud Book 12, Hadith Number 2891.

Chapter : On the share of grandfather from inheritance.

Narated By Ma’qil ibn Yasar : Al-Hasan reported that Umar asked: Which of your knows what share the Apostle of Allah (PBUH) had given to the grandfather from the estate? Ma’qil ibn Yasar said: The Apostle of Allah (PBUH) gave him a sixth. He asked: Along with whom? He replied: I do not know. He said: You do not know; what is the use then?