Musannaf Ibn Abi Shayba 18:657

Abu Bakr narrated to us, he said: Muhammad ibn Bishr narrated to us, from Ibn Jurayj, from Abd al-Karim, that a stallion (camel) attacked a man and killed him. It was brought before Abu Bakr, and he imposed a fine for it, and he said: "It is an animal that has no intellect (i.e., it is not legally responsible)."