Narrated Anas: Bilal was ordered to repeat the wording of the Adhan for prayers twice, and to pronounce the wording of the Iqama once except "Qad-qamat-is-salat".
Hadith ReferenceSahih Bukhari / The Book of Adhan / Hadith: 605
Hadith Gradingمحدثین:أحاديث صحيح البخاريّ كلّها صحيحة