Kharijah bin Zayd (may Allah have mercy on him) narrates from his father that the meanings and principles of these inheritance shares are from Sayyiduna Zayd bin Thabit (may Allah be pleased with him), and their explanation is from Abu al-Zinad. He said: A man inherits half from his wife if she has not left children or son's children. If she has left children or son's children, male or female, the man takes a quarter. And the wife inherits a quarter from her husband if he has not left children or son's children; and if he has left children or son's children, the wife inherits an eighth.
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الفرائض / 12293