Musnad Ahmad 27:723

Yahya narrated to us, from Ubaydullah, Nafi’ informed me, from Ibn Umar, who said: A man called out to the Messenger of Allah (ﷺ): "From where do you command us to enter into Ihram?" He said: "The people of Medina enter into Ihram from Dhu al-Hulayfah, the people of Syria from al-Juhfah, and the people of Najd from Qarn." Abdullah said: And they claim that he said: "And the people of Yemen from Yalamlam."