Musnad Ahmad 22:10

Yazid ibn Abi Hakim al-Adani narrated to us, al-Hakam—meaning Ibn Aban—narrated to me, I heard Ikrimah saying: Al-Fadl ibn Abbas said: "When the Messenger of Allah (may Allah bless him and grant him peace) departed from Arafat, and I was with him, we reached the mountain pass. He dismounted and performed ablution. Then we rode on until we arrived at al-Muzdalifah."