Musannaf Ibn Abi Shayba 26:498

Waki’ narrated to us, he said: Shu’bah narrated to us, from Abu Ma’shar, who said: Ibrahim used to say regarding the father: "He has one-sixth of the *wala’* (right of inheritance/patronage), and for the son is five-sixths of the *wala’*." Shu’bah said: I said to Abu Ma’shar, "Did you hear it from Ibrahim saying it?" He said, "I heard it." And Mughirah said, "I heard it from Ibrahim saying it."