It is reported from Sa'id bin al-Musayyab (may Allah have mercy on him) that Zayd bin Thabit (may Allah be pleased with him) would not assign a share to the grandmother when her son, that is, the father of the deceased, was present.
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الفرائض / 12282