Musnad Ahmad 27:229

Yahya narrated to us, from Sufyan, Abu Ishaq narrated to me, from Abdullah ibn Malik, that Ibn Umar prayed Maghrib and Isha at Jam’ (Muzdalifah) with a single iqamah. Abdullah ibn Malik said to him: "O Abu Abd al-Rahman, what is this prayer?" He replied: "I prayed it with the Messenger of Allah, peace and blessings of Allah be upon him, in this place with a single iqamah."