The Book of Prayer
Bulugh al-Maram #216
كتاب الصلاة
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
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).
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
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).
— Bulugh al-Maram, Hadith 216