Musannaf Ibn Abi Shayba 27:872

Muhammad ibn al-Hasan narrated to us, he said: al-Walid narrated to us, from Simak ibn Harb, he said: I reached two thousand [men] from Banu Asad who had witnessed al-Qadisiyyah in two thousand [men], and their banners were in the hand of Simak, the companion of the mosque.