Muwatta Imam Malik (Riwayat Yahya)

Imam Malik, may Allah have mercy on him, said: According to us, it is a unanimous ruling that if the deceased leaves behind a son or a grandson, then the father will receive one-sixth. If the deceased does not have a son or a grandson, then after giving the shares to all the rightful heirs, whatever remains—whether it is one-sixth or more—will go to the father. If, after distributing the shares of the rightful heirs, one-sixth does not remain, then the father will be given one-sixth as an obligatory share(1). The mother of the deceased will receive one-sixth when the deceased has children, or the children of his son, or two or more brothers or sisters, whether full, paternal, or maternal(2). Otherwise, the mother will receive a full one-third if the deceased has no children, no son’s children, and no two brothers or two sisters. However, in two cases: one is that if the deceased leaves behind a wife and parents, the wife will receive one-fourth, and the mother will receive one-third of what remains, that is, one-fourth of the total estate. The second is that if a woman dies and leaves behind a husband and parents, the husband will receive half, and after that, the mother will receive one-third of what remains, that is, one-sixth of the total estate, because Allah, Glorified and Exalted is He, says in His Book: “For each of the parents of the deceased, one-sixth of the inheritance if the deceased has children. If he has no children and his parents are his heirs, then his mother will receive one-third, and the rest will go to the father. If the deceased has brothers, then the mother will receive one-sixth.”
Imam Malik, may Allah have mercy on him, said: The established Sunnah is that “brothers” refers to two brothers, or two sisters, or two or more.