Then two shares remain for three, so it is valid from one hundred and eight, then it reduces by reduction (ikhtisar) to fifty-four; for this reason, it is called 'the shortened one'. A mother, a sister from both parents, two brothers and a sister from a father, and a grandfather; its origin is from six, then it shifts to eighteen, and there remains for the child of the father one share out of five; you multiply them by eighteen, resulting in ninety, and it is called 'the ninety-fold [issue] of Zayd'. In this entire section, the grandmother is like the mother, because each of them has the sixth.

1029 - Issue: He said: (And if there is a daughter, a sister, and a grandfather, the daughter has the half, and what remains is between the grandfather and the sister, in three shares: the grandfather has two shares, and the sister has one share.)

It was only like this because the division (muqasama) here is more favorable for the grandfather. Ali, may Allah be pleased with him, said: The daughter has the half, the grandfather has the sixth, and the remainder is for the sister. According to Ibn Mas'ud, the remainder after the fixed share of the daughter is [divided] between the grandfather and the sister into two halves, because if either of them were alone, they would take the property by residuary inheritance (ta'sib), so when they come together, they divide it, just as if there were a brother in her place. As for Ali, he based it on his principle that sisters do not perform the division with the grandfather, but rather a share is fixed for them; so he did not fix a share for her here, because the sister with the daughter is a residuary heir, and he gave the grandfather the sixth, just as if he were alone with her, and he assigned the remainder to her. For us, the grandfather performs the division with the sister, and he takes the equivalent of her [share] if a brother is with her; likewise, [he does so] if she is alone. This is one of the four-way divisions (murabba'at) of Ibn Mas'ud.

Section: A daughter, a brother, and a grandfather; the remainder after the fixed share of the daughter is [divided] between them into two halves. If his sister is with him, the remainder is between them over five. If there are two brothers, or a brother and two sisters, or four sisters, a third of the remainder, the sixth, and the division are equal. If they increase [in number], he has no advantage in the division, so he takes the sixth, and the remainder is for them. If they are from both sides [of the lineage], the child of the father has nothing, and the child of both parents takes the entire remainder. A daughter, two sisters, and a grandfather; the remainder is between the grandfather and the two sisters over four, and it is valid