Musnad Ahmad 27:1797

Jarir narrated to us, from Sadaqah ibn Yasar, I heard Ibn Umar saying: "The Messenger of Allah (peace and blessings of Allah be upon him) appointed Dhu al-Hulayfah for the people of Medina, and al-Juhfah for the people of Syria." He said: "And for the people of Najd, Qarn; and for the people of Yemen, Yalamlam." It was said to him: "And Iraq?" He said: "There was no Iraq in those days."