Musannaf Ibn Abi Shayba 26:214

Ibn Fudayl narrated to us, from Bassam, from Fudayl, from Ibrahim, regarding a woman who left behind her sister (from her father and mother), her grandmother, and her mother: The sister (from her father and mother) gets one-half, the mother gets one-third, and the grandmother gets one-sixth, according to the opinion of Ali. Abdullah used to say: The mother gets one-sixth, the grandfather gets one-third, and the sister gets one-half. Abdullah used to say: "Allah would not see me preferring a grandfather in this obligatory share, nor in any other of the prescribed limits." Zayd used to give the mother one-third, and the sister one-third of what remained. Zayd divided it into nine shares: for the mother one-third (three shares), for the sister one-third of what remained (two shares), and for the grandfather four shares. Uthman used to divide it among them in thirds: for the mother one-third, for the sister one-third, and for the grandfather one-third. Ibn Abbas used to say: The grandfather is in the position of the father.