Yahya bin Sa'id al-Ansari يحيى بن سعيد الأنصاري · The Chapters on Jihad

“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.’”

“The Muslim is obliged to obey (the ruler) whether he likes it or not, unless he is commanded to commit an act of disobedience. If he is commanded to commit a sin then he should neither listen nor obey.”