Sahih Bukhari Volume 4, Book 54, Hadith Number 517.

Narated By Abdur-Rahman bin Abdullah bin Abdur-Rahman bin Abi Sasaa Ansari : That Abu Said Al-Khudri said to his father. “I see you are fond of sheep and the desert, so when you want to pronounce the Adhan, raise your voice with it for whoever will hear the Adhan whether a human being, or a Jinn, or anything else, will bear witness, in favor on the Day of Resurrection.” Abu Said added, “I have heard this from Allah’s Apostle.”