Musnad Ahmad 26:866

Muhammad ibn Ja'far narrated to us, Shu'bah narrated to us, from 'Asim ibn Bahdalah, from Abu Wa'il, narrating from 'Abdullah, who said: We used to speak during the prayer. So I came to the Messenger of Allah, peace and blessings of Allah be upon him, and I greeted him, but he did not return the greeting to me. Then, what had passed and what had occurred [of anxiety] seized me. The Messenger of Allah, peace and blessings of Allah be upon him, said: "Indeed, Allah brings about for His Prophet whatever He wills" — Shu'bah said: And I think he said: "from whatever He wills" — "and indeed, among what He has brought about for His Prophet, peace and blessings of Allah be upon him, is that you should not speak during the prayer."