Sayyiduna Abu Mahdhurah (may Allah be pleased with him) narrates: I said: "O Messenger of Allah, teach me the way of the adhan." So he passed his hand over the front part of my head and said: "Say: 'Allahu akbar, Allahu akbar, Allahu akbar, Allahu akbar,' raising your voice with it. Then say: 'Ashhadu an la ilaha illallah, ashhadu an la ilaha illallah, ashhadu anna Muhammadan rasulullah, ashhadu anna Muhammadan rasulullah,' lowering your voice with it. Then say: 'Ashhadu an la ilaha illallah, ashhadu an la ilaha illallah, ashhadu anna Muhammadan rasulullah, ashhadu anna Muhammadan rasulullah, hayya 'ala al-salah, hayya 'ala al-salah, hayya 'ala al-falah, hayya 'ala al-falah.' Then, if it is the Fajr prayer, say: 'Al-salatu khayrun min al-nawm, al-salatu khayrun min al-nawm (Prayer is better than sleep), Allahu akbar, Allahu akbar, la ilaha illallah.'"
Hadith Referenceالمعجم الكبير للطبراني / باب السين / 6705