Sahih Muslim
Sahih Muslim 378 d
Book 4: The Book of Prayers
Chapter 2 The Command to say the phrases of the Adhan twice and the phrases of the iqamah once, except the phrase, "Prayer is about to begin," which is to be said twice
باب الأَمْرِ بِشَفْعِ الأَذَانِ وَإِيتَارِ الإِقَامَةِ
Sahih Muslim 378 d
Anas reported: Bilal was commanded (by the Holy Prophet) to repeat the phrases twice in Adhan, and once in lqama.
وَحَدَّثَنِي عُبَيْدُ اللَّهِ بْنُ عُمَرَ الْقَوَارِيرِيُّ، حَدَّثَنَا عَبْدُ الْوَارِثِ بْنُ سَعِيدٍ، وَعَبْدُ الْوَهَّابِ بْنُ عَبْدِ الْمَجِيدِ، قَالاَ حَدَّثَنَا أَيُّوبُ، عَنْ أَبِي قِلاَبَةَ، عَنْ أَنَسٍ، قَالَ أُمِرَ بِلاَلٌ أَنْ يَشْفَعَ، الأَذَانَ وَيُوتِرَ الإِقَامَةَ .
More hadith from this chapter
Hadith text, translations and grading are courtesy of Sunnah.com.