Musannaf Ibn Abi Shayba 18:22

Abu Bakr narrated to us, he said: Muhammad ibn Bakr narrated to us, from Ibn Jurayj, he said: Abd al-Karim ibn Abi al-Mukhariq narrated to us, from al-Hasan, he said: If the owner of the cows and the sheep wishes, he may give camels [as Zakat].