Musannaf Ibn Abi Shayba 26:20

Waki’ narrated to us, from Hisham al-Dastawa’i, from Qatada, from Sa’id ibn al-Musayyib, that Zayd ibn Thabit was asked about a woman and two parents. He gave the woman a quarter, and the mother a third of what remained, and what remained was for the father.