Musannaf Ibn Abi Shayba 27:836

Waki’ narrated to us, from Isma’il, from Qays, who said: ‘Amr ibn Ma’di Karib used to pass by during the days of al-Qadisiyyah while we were in rows, and he would say: “O assembly of Arabs, be lions! For the Persian is only a billy goat after he throws his spear.”