Musannaf Ibn Abi Shayba 28:1074

Abu Bakr ibn Ayyash narrated to us, from Asim, from al-Harith ibn Hassan, who said: I arrived in Medina. And behold, the Prophet, may Allah bless him and grant him peace, was upon the pulpit, and Bilal was standing before him, girded with a sword. And behold, there were black banners. I said, "Who is this?" They said, "Amr ibn al-Aas, he has arrived from a military expedition."