Musnad Ahmad 25:337

Yazid ibn Abi Hakim narrated to us, Al-Hakam—meaning Ibn Aban—narrated to us, he said: I heard Ikrimah saying: Ibn Abbas said: "The *‘anzah* (a short spear) was planted in front of the Prophet, may Allah bless him and grant him peace, at Arafat, and he prayed facing it, while a donkey was passing behind the *‘anzah*."