Musannaf Ibn Abi Shayba 33:605

Abu Usama narrated to us, from Hisham ibn Urwah, from Wahb ibn Kaysan, who said: A man from the people of Iraq wrote to Ibn al-Zubayr when he was given the pledge of allegiance: "Peace be upon you. I praise to you Allah, other than whom there is no god. To proceed: The people of obedience to Allah and the people of goodness have a sign by which they are known, and it is known among them through enjoining good, forbidding evil, and acting in obedience to Allah. And know, O Imam, that the market is like the people who come to it; whatever is pure in it comes to it. If it is righteous, the people of righteousness come to it with their righteousness; and if it is wicked, the people of wickedness come to it with their wickedness."