Musnad Ahmad 30:3745

Abu Sa’id narrated to us, Za’idah narrated to us, al-A’mash narrated to us, from Abu Salih, from Abu Hurayrah, that the Messenger of Allah (peace and blessings of Allah be upon him) said: "When the Shaytan hears the caller calling to prayer, he departs while having a flatulence, so that he does not hear the sound. When he finishes, he returns and whispers. When he (the caller) begins the iqamah, he does the same thing."