Imam Malik's Muwatta, Chapter: Faraid

Malik said, "The inheritance of a husband from a wife when she leaves no children or grandchildren through sons is a half. If she leaves children or grandchildren through sons, male or female, by her present or previous husbands, the husband has a quarter after bequests or debts. The inheritance of a wife from a husband who does not leave children or grandchildren through sons is a quarter. If he leaves children or grandchildren through sons, male or female, the wife has an eighth after bequests and debts. That is because Allah, the Blessed, the Exalted! said in His Book, 'You have a half of what your wives leave if they have no children. If they have children, you have a fourth of what they leave after bequests and debts. They have a fourth of what you leave if you have no children. If you have children, they have an eighth after bequests or debts.' " (Sura4ayat 11).