Al-Hasan al-Basri (may Allah have mercy on him) relates that Sayyiduna Umar (may Allah be pleased with him) asked: Who knows what the Messenger of Allah (peace and blessings be upon him) decided concerning the grandfather? Sayyiduna Ma'qil bin Yasar (may Allah be pleased with him) said: I (know). Umar (may Allah be pleased with him) asked: How much is his share? He said: "One sixth." Umar (may Allah be pleased with him) asked: Who else shares with him? He said: I do not know. Umar (may Allah be pleased with him) said: Then you know nothing!
Hadith Referenceالمعجم الكبير للطبراني / باب الميم / 17597