Musannaf Ibn Abi Shayba 2:30

Abu Bakr narrated to us, he said: Abu al-Ahwas narrated to us, from Abd al-Aziz ibn Rufay’, he said: The leader (guide) of Abu Mahdhura narrated to me that his Adhan was two by two, and his Iqama was once, and the conclusion of his Adhan was: "Allah is the Greatest, Allah is the Greatest, there is no god but Allah."