Bulugh al-Maram 2 The Book of Prayer كتاب الصلاة 37

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 . 1 – صحيح. رواه البخاري (605)، ومسلم (378).

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].