Sayyiduna Salamah bin al-Akwa' (may Allah be pleased with him) states: In the blessed time of the Prophet (peace and blessings be upon him), the words of the adhan were said twice each and the words of the iqamah once each.
Imam al-Tabarani recorded this narration in al-Mu'jam al-Kabir, and its chain is hasan (good).
Hadith Referenceمجمع الزوائد ومنبع الفوائد / كتاب الصلاة / 1863