Sahih al-Bukhari 603
Book 10: Call to Prayers (Adhaan) · Hadith 1
Hadith text
Narrated Anas:The people mentioned the fire and the bell (they suggested those as signals to indicate the starting of prayers), and by that they mentioned the Jews and the Christians. Then Bilal was ordered to pronounce Adhan for the prayer by saying its wordings twice, and for the Iqama (the call for the actual standing for the prayers in rows) by saying its wordings once. (Iqama is pronounced when the people are ready for the prayer)
Anas (رضی اللہ عنہ) se riwayat hai ke logon ne aag aur ghanti ka zikar kiya (namaz ka waqt bataane ke liye), aur isse woh Yahudi aur Isaiyon ka tareeqa samajhte the. Phir Bilal ko hukum diya gaya ke woh Adhan ke alfaaz do-do baar aur Iqama ke alfaaz ek-ek baar kahen (Iqama tab kahi jaati hai jab log namaz ke liye taiyaar hon).
Sahih al-Bukhari 603 · Book 10, Hadith 1