Musnad Ahmad 30:2414

Yahya ibn Sa'id narrated to us, from Shu'bah, who said: Musa ibn Abi 'Uthman narrated to me, who said: Abu Yahya, the freed slave of Ja'dah, narrated to me, who said: I heard Abu Hurairah, that he heard from the mouth of the Messenger of Allah, peace and blessings of Allah be upon him, saying: "The mu'adhdhin is forgiven for the extent of his voice, and everything wet and dry bears witness for him. And the one who attends the prayer, twenty-five good deeds are written for him, and what is between them is expiated for him."