Musnad Ahmad 27:5

Hushaym narrated to us, Isma'il ibn Abi Khalid narrated to us, from Abu Ishaq, from Sa'id ibn Jubayr, who said: We were with Ibn 'Umar when he departed from 'Arafat to Jam' (Muzdalifah). He prayed Maghrib with us, and then proceeded. Then he said: "The prayer," and he prayed two rak'ahs. Then he said: "This is how the Messenger of Allah, may Allah bless him and grant him peace, did in this place, just as I have done."