Musnad Abu Ya'la al-Mawsili 154:161

Abu Khaythama narrated to us, Ishaq bin Yusuf narrated to us, from Sufyan, from Salamah bin Kuhayl, from Sa'id bin Jubayr, from Ibn 'Umar: That he prayed Maghrib and Isha at Jam' (Muzdalifah) with one iqamah. Then he said: "Thus I saw the Messenger of Allah, may Allah bless him and grant him peace, doing it."