It is narrated from Abdullah bin Malik al-Azdi: I prayed with Sayyiduna Ibn Umar (may Allah be pleased with them both) at Muzdalifah three rak'ahs of Maghrib and two rak'ahs of Isha with one iqamah. Malik bin Khalid said to him: O Abu Abd al-Rahman, what prayer is this? He said: I prayed with the Messenger of Allah (peace and blessings be upon him) at this place with one iqamah.
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الصلاة / 1882