أَخْبَرَنَا عَمْرُو بْنُ عَلِيٍّ، قَالَ حَدَّثَنَا يَحْيَى، قَالَ حَدَّثَنَا شُعْبَةُ، قَالَ حَدَّثَنِي أَبُو جَعْفَرٍ، عَنْ أَبِي الْمُثَنَّى، عَنِ ابْنِ عُمَرَ، قَالَ كَانَ الأَذَانُ عَلَى عَهْدِ رَسُولِ اللَّهِ صلى الله عليه وسلم مَثْنَى مَثْنَى وَالإِقَامَةُ مَرَّةً مَرَّةً إِلاَّ أَنَّكَ تَقُولُ قَدْ قَامَتِ الصَّلاَةُ قَدْ قَامَتِ الصَّلاَةُ ‏.‏

It was narrated that Ibn 'Umar said: "At the time of the Messenger of Allah (PBUH) the phrases of the Adhan were said twice and the phrases of the Iqamah were said once, except that you should I say: 'Qad Qamatis-Salah, Qad Qamatis-Salah (prayer is about to begin, prayer is about to begin).'" Translation Not Available

Book reference: Sunan An Nisai Book 7 Hadith 635
Web reference: Sunan An Nisai Volume 1 Book 7 Hadith 629