It is narrated from Sayyiduna Abdullah bin Umar (may Allah be pleased with them both) that in the time of the Prophet (peace and blessings be upon him) the adhan was twice each and the iqamah once each; when the muezzin says 'Qad qamat al-salah' (The prayer has been established), he should say it twice.
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الصلاة / 1960