Muwatta Malik: Book 27, Hadith 3

Malik said, “The generally agreed on way of doing things among us about which there is no dispute and what I have seen the people of knowledge in our city doing is that when a father inherits from a son or a daughter and the deceased leaves children, or grandchildren through a son, the father has a fixed share of one sixth. If the deceased does leave any children or male grandchildren through a son, the apportioning begins with those with whom the father shares in the fixed shares. They are given their fixed shares. If a sixth or more is left over, the sixth and what is above it is given to the father, and if there is less than a sixth left, the father is given his sixth as a fixed share, (i.e. the other shares are adjusted.)

“The inheritance of a mother from her child, if her son or daughter dies and leaves children or male or female grandchildren through a son, or leaves two or more full or half siblings is a sixth. If the deceased does not leave any children or grandchildren through a son, or two or more siblings, the mother has a whole third except in two cases. One of them is if a man dies and leaves a wife and both parents. The wife has a fourth, the mother a third of what remains, (which is a fourth of the capital). The other is if a wife dies and leaves a husband and both parents. The husband gets half, and the mother a third of what remains, (which is a sixth of the capital). That is because Allah, the Blessed, the Exalted, says in His Book, ‘His two parents each have a sixth of what he leaves if he has children. If he does not have children, and his parents inherit from him, his mother has a third. If he has siblings, the mother has a sixth.’ (Sura 4 ayat 11). The sunna is that the siblings be two or more.”