Musnad Ahmad 27:1402

'Affan narrated to us, Shu'bah narrated to us, he said: 'Abdullah ibn Dinar informed me, he said: I heard Ibn 'Umar saying: "The Messenger of Allah (may Allah bless him and grant him peace) appointed Dhu al-Hulayfah for the people of Medina, Qarn for the people of Najd, and al-Juhfah for the people of Syria." And they claimed that he appointed Yalamlam for the people of Yemen.