Sunan Abi Dawud Book 2, Hadith 120
The words of adhan were pronounced from the time of the Messenger of Allah (ﷺ) twice in pairs (i.e. four times) each, and the words of iqamah were pronounced once in pairs (twice each), except that the phrase "The time for prayer has come" would be pronounced twice. When we heard iqamah, we would perform ablution, and go out for prayer. Shu'bah said: I did not hear AbuJa'far narrating any other tradition except this one.
I narrated this tradition to Ayyub who said: “Except IQAMAH”.
This tradition has been narrated by Abu Ja’far, the mu’adhdhin of ‘Uryan mosque (at Kufah), from Abu al-Muthanna, the mu’adhdhin of masjid al-akbar (at kufah) on the authority of Ibn ‘Umar. The rest of the tradition was transmitted in a like manner.