Musnad Ahmad 27:1120

Muhammad ibn Ja’far narrated to us, Shu’bah narrated to us, I heard Abu Ja’far—meaning the Mu’adhdhin—narrating from Muslim Abu al-Muthanna, narrating from Ibn ‘Umar, who said: "The Adhan during the time of the Messenger of Allah (ﷺ) was only two times"—and Hajjaj said: meaning two times, two times—"and the Iqamah was once, except that he would say: 'Qad qamat al-salah, qad qamat al-salah' (The prayer has been established, the prayer has been established). And we, when we heard the Iqamah, would perform ablution, then we would go out to the prayer." Shu’bah said: "I do not memorize anything other than this."