Al-Harith bin Hassan al-Bakri (may Allah be pleased with him) said: I came to the Prophet (peace and blessings be upon him) while he (peace and blessings be upon him) was on the pulpit, and Bilal (may Allah be pleased with him) was standing with a sword hung at his side, and at that time the banners were black, and the people were saying: This is Amr bin al-As (may Allah be pleased with him) who has arrived.
Hadith Referenceالسنن الكبرى للبيهقي / كتاب قسم الفيء والغنيمة / 13068