Musannaf Ibn Abi Shayba 3:6005

Ghundar narrated to us, from Shu'bah, from Mansur, who said: I heard Ibrahim ibn Abi Hasan, that he heard Mujahid say regarding this verse: "And when the Qur'an is recited, then listen to it and pay attention," He said: In the prayer and the sermon on the day of Friday.