Musnad Ahmad 27:1083

Muhammad narrated to us, Shu'bah narrated to us, from 'Abdullah ibn Dinar, who said: I heard Ibn 'Umar narrating: "That the Messenger of Allah (ﷺ) appointed Dhu al-Hulayfah for the people of Medina, Qarn for the people of Najd, and al-Juhfah for the people of Sham." And 'Abdullah said: "And they claimed that the Messenger of Allah (ﷺ) said: 'And for the people of Yemen, Yalamlam.'"