Musannaf Ibn Abi Shayba 26:74

Abu Mu'awiyah narrated to us, from al-A'mash, from Ibrahim, who said: Abdullah and Umar used to include [the siblings in the inheritance]. He said: And Ali used to not include [them]. Abu Bakr said: And this is from the six shares: for the husband is the half, which is three shares; and for the mother is the sixth; and for the siblings from the mother is the third, which is two shares.