Musannaf Ibn Abi Shayba 18:1166

Abu Bakr narrated to us, he said: Ibn Fudayl narrated to us, from Ash'ath, from Ibn Sirin, who said: A man carried his son on a horse to teach him to ride, then he prodded it and shouted at it, so it killed him. He (the judge) placed his blood money upon his (the father's) paternal relatives (aqilah), and he did not allow the father to inherit anything.