Musannaf Ibn Abi Shayba 2:163

Mu'tamir narrated to us, from Ibn 'Awn, from Ibrahim, who said: They used to be of the opinion that if one prays in the city alone, the iqamah suffices him, except for the dawn (Fajr) prayer, for he should perform the adhan and the iqamah. He said: And Ibn Sirin used to say the same.