Musnad Ahmad 27:1670

Ya'qub ibn Ibrahim narrated to us, my father narrated to us, from Ibn Ishaq, Nafi' narrated to me, from Ibn 'Umar, who said: "The Messenger of Allah (peace and blessings of Allah be upon him) set out from Mina when he had prayed the morning prayer on the morning of the day of 'Arafah, until he came to 'Arafah and descended at Namirah, which is the place where the Imam used to descend at 'Arafah. Then, when it was time for the noon prayer, the Messenger of Allah (peace and blessings of Allah be upon him) set out in the early part of the afternoon, and he combined the noon and afternoon prayers. Then he addressed the people, then he set out and stood at the station of 'Arafah."