سنن ابن ماجه

It was narrated that Harith bin Hassan said: “I came to Al-Madinah and saw the Prophet (ﷺ) standing on the pulpit, and Bilal standing in front of him, with his sword by his side, and (I saw) a black flag. I said: ‘Who is this?’ He said: ‘This is ‘Amr bin ‘As, who has just come back from a campaign.’”