Sahih Bukhari
Call to Prayers (Adhaan)
Volume: 001 / Book Number: 011 / Hadith Number: 606
Narrated 'Aun bin Abi Juhaifa:
My father said, "I saw Allah's Apostle at a place called Al-Abtah. Bilal came and informed him about the prayer and then came out with an Anza and planted it in front of Allah's Apostle at Al-Abtah and pronounced the Iqama."