Musannaf Ibn Abi Shayba 3:2839

Abu Bakr narrated to us, he said: Waki’ narrated to us, from Sufyan, from Abu Ishaq, from Hilal bin Qais, from Zaid bin Suhan, he said: If you hear a man speaking while the Imam is delivering the sermon on Friday, then if he is near you, nudge him. And if he is far from you, gesture to him, and do not throw pebbles at him.