Call to Prayers (Adhaan) 
Bukhari :: Book 1 :: Volume 11 :: Hadith 585
Narrated Abu Said Al-Khudri:
Allah's Apostle said, "Whenever you hear the Adhan, say what the Mu'adhdhin is saying.
Call to Prayers (Adhaan)
Bukhari :: Book 1 :: Volume 11 :: Hadith 585
Narrated Abu Said Al-Khudri:
Allah's Apostle said, "Whenever you hear the Adhan, say what the Mu'adhdhin is saying.