(a) Ash'ath bin Sulaym narrates from his father: I came with Sayyiduna Ibn Umar (may Allah be pleased with them both) from Arafat to Muzdalifah; we kept on saying 'Allahu akbar' (Allah is the Greatest) and 'La ilaha illallah' (There is no god but Allah) until we reached Muzdalifah. He gave the adhan and the iqamah, or ordered a man, who gave the adhan and the iqamah; then he led us in three rak'ahs of Maghrib, then turned towards us, then led us in two rak'ahs of Isha, then called for his dinner. (b) In the hadith of Ilaj bin Amr it says: I prayed in this way with the Prophet (peace and blessings be upon him). (c) It is narrated from Sayyiduna Umar bin al-Khattab and Sayyiduna Abdullah bin Mas'ud (may Allah be pleased with them both) that they prayed the two prayers separately in the time of Isha, with one adhan and one iqamah.
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الصلاة / 1885