Musannaf Ibn Abi Shayba 33:956

Affan narrated to us, he said: Hammad bin Zayd narrated to us, he said: Ayyub narrated to us, he said: Muslim bin Yasar said: Abu Qilabah was from the non-Arabs (Ajam). He was the Mobad al-Mobadan (the chief priest of the Zoroastrians).