Narrated Anas (RA):

Bilal was commanded to announce the Adhan (each phrase) twice and the Iqamah (each phrase) once except "The prayer stood ready to begin" (to be pronounced twice). [Agreed upon; but Muslim did not mentioned the exception].

وَعَنْ أَنَسِ]بْنِ مَالِكٍ] ‏- رضى الله عنه ‏- قَالَ: { أُمِرَ بِلَالٌ أَنْ يَشْفَعَ اَلْآذَانَ, وَيُوتِرَ اَلْإِقَامَةَ, إِلَّا اَلْإِقَامَةَ, يَعْنِي قَوْلَهُ: قَدْ قَامَتِ اَلصَّلَاةُ } مُتَّفَقٌ عَلَيْهِ, وَلَمْ يَذْكُرْ مُسْلِمٌ اَلِاسْتِثْنَاءَ [1]‏ .‏