Musnad Abu Ya'la al-Mawsili 155:19

Zakariya ibn Yahya al-Wasiti narrated to us, Rawh ibn 'Ubadah narrated to us, Ibn Jurayj narrated to us, he said: Ibn Shihab narrated to me, from 'Umar ibn 'Abd al-'Aziz, from Ibrahim ibn 'Abd Allah ibn Qariz, and from Sa'id ibn al-Musayyib, from Abu Hurayrah, he said: I heard the Messenger of Allah, peace and blessings of Allah be upon him, saying: "If you say to your companion, 'Be silent,' while the Imam is delivering the sermon, then you have engaged in idle talk."