Musannaf Ibn Abi Shayba 37:642

Yazid ibn Harun narrated to us, he said: Hammad informed us, from al-Jurayri, from Ibn al-Muthanna, from Abu Umamah, who said: The Hour will not be established until the evil ones of the people of al-Sham move to Iraq, and the best of the people of Iraq move to al-Sham.