Musannaf Ibn Abi Shaybah 33377 — When he leaves his grandfather

And Sayyiduna Ali (may Allah be pleased with him) used to give the full sister half of the wealth and divide the remaining half between the brothers and the grandfather, in such a way that the grandfather was counted as one of the brothers, so long as the grandfather's portion was not less than a sixth. If there is one brother, the remaining half is to be divided between the two of them; if there are two, the half is to be divided between those two; and if there are three, a sixth of the wealth is for the grandfather and the remaining wealth is for the brothers.