Musannaf Ibn Abi Shayba 26:30

Ibn Idris narrated to us, from al-A’mash, from Ibrahim, from al-Aswad, who said: Abdullah said: Verily, when Umar would take a path, and we would take it, we would find it easy. And he was approached regarding a woman and two parents. So he gave the woman a fourth, and the mother a third of what remained, and what remained was for the father.