Sayyiduna Zayd bin Thabit (may Allah be pleased with him) used to say: When the grandmother from the mother's side is nearer, she is more entitled than the one from the father's side, and she alone is entitled to the sixth; and when the grandmother from the father's side is nearer, I will make the two of them partners. It was said: How did the grandmother from the mother's side reach this position? He said: Because the share of the grandmothers is the sixth on account of the mother's sixth.
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الفرائض / 12365