Musnad Abu Ya'la al-Mawsili 110:202

Abu Bakr narrated to us, Muhammad ibn Fudayl narrated to us, from Hajjaj, from Abu Salih, from Ibn Abbas, who said: The Prophet, may Allah bless him and grant him peace, distributed [the spoils] on the day of Hunayn, giving the horseman three shares and the foot soldier one share.