(6) باب إِفْرَادِ الإِقَامَةِ
It was narrated that Anas said:
"Bilal was commanded to say the phrases of the Adhan twice and the phrases of the Iqamah once."
Reference: Sunan Ibn Majah 730
In-book reference: Book 3, Hadith 25
English translation: Vol. 1, Book 3, Hadith 730