Musnad Ahmad 27:1940

Rawh narrated to us, Shu'bah narrated to us, I heard Abu Ishaq, I heard Abdullah ibn Malik, he said: "I prayed with Ibn Umar at Jam' (Muzdalifah). He performed the iqamah, then prayed Maghrib as three rak'ahs, then prayed Isha as two rak'ahs, with a single iqamah." He said: Khalid ibn Malik asked him, and he said: "Indeed, the Messenger of Allah (peace and blessings of Allah be upon him) did the same as this in this place."