Call to Prayers (Adhaan)

Bukhari :: Book 1 :: Volume 11 :: Hadith 661

Narrated Ibn 'Umar:

When the earliest emigrants came to Al-'Usba a place in Quba', before the arrival of the Prophet- Salim, the slave of Abu Hudhaifa, who knew the Qur'an more than the others used to lead them in prayer.