Abu al-Muthanna said: I heard Sayyiduna Ibn Umar (may Allah be pleased with them both) say: "In the time of the Prophet (peace and blessings be upon him) the adhan was twice each and the iqamah once each; when he said 'Qad qamat al-salah' (The prayer has been established), he would say it twice. When any of us heard the iqamah, he would perform ablution and then come out."
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الصلاة / 1961