Abidah al-Salmani (may Allah have mercy on him) said: Sayyiduna Ali (may Allah be pleased with him) used to give the grandfather a third alongside the brothers, and Sayyiduna Umar (may Allah be pleased with him) used to give him a sixth. Then Umar wrote to Abdullah (may Allah be pleased with them both): "We fear that we have been unfair to the grandfather, so give him a third." When Sayyiduna Ali (may Allah be pleased with him) came here, he gave him a sixth. Abidah (may Allah have mercy on him) said: The opinion of the two of them in agreement is dearer to me than the opinion of either one of them in disagreement.
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الفرائض / 12435