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 أَبِي جُحَيْفَةَ - رضى الله عنه - قَالَ: { رَأَيْتُ بِلَالاً يُؤَذِّنُ وَأَتَتَبَّعُ فَاهُ, هَاهُنَا وَهَاهُنَا, وَإِصْبَعَاهُ فِي أُذُنَيْهِ } رَوَاهُ أَحْمَدُ, وَاَلتِّرْمِذِيُّ وَصَحَّحَهُ 1 .1 - صحيح. رواه أحمد (4/308-309)، والترمذي (197)، وقال الترمذي: "حديث حسن صحيح".
Narrated Narrated Abu Juhaifa (RA):
I saw Bilal calling for prayer and I would follow (looking at) his mouth (as he turned it) this (right) side and that (left) side with his fingers in his ears.