Musannaf Ibn Abi Shayba 3:6004

Abu Khalid al-Ahmar narrated to us, from Ash'ath, from Ibrahim, who said: The Prophet (peace and blessings of Allah be upon him) was reciting, and a man was reciting. Then Allah the Exalted revealed: "And when the Qur'an is recited, then listen to it and pay attention."