Sunan An-Nasai, Chapter: The Book of the Adhan (The Call to Prayer)

that his father told him that Abu Said Al-Khudri said to him: "I see that you love sheep and the desert. When you are with your sheep or in the desert and you call the Adhan for prayer, then raise your voice, for no human, Jinn or anything else hears the voice of the Muadhdhin as far as it reaches, but it will bear witness for him on the Day of Resurrection." Abu Sa'eed said: "I heard it from the Messenger of Allah (saw)." (Sahih)