Musannaf Ibn Abi Shayba 2:257

Abu Bakr narrated to us, he said: Muhammad ibn Mus'ab narrated to us, from al-Awza'i, from Yahya, from Abu Salamah, from Abu Hurayrah, who said: The Prophet (peace and blessings of Allah be upon him) said: "When the mu'adhdhin calls for prayer, the Shaytan turns his back, having a passing of wind. When he finishes, he returns. Then, when the iqamah is called for it, he turns his back."