Musnad Ahmad 1034:72

Abdullah ibn Numayr narrated to us, Razin al-Juhani narrated to us, Abu al-Ruqad narrated to me, he said: I went out with my master while I was a boy, and I reached Hudhayfah while he was saying: "A man would speak a word during the time of the Messenger of Allah, peace and blessings of Allah be upon him, and he would become a hypocrite. And I hear it from one of you in a single sitting four times. You must enjoin the good, and you must forbid the evil, and you must encourage one another to do good, or Allah will surely overwhelm you all with a punishment, or He will surely appoint over you your worst, then your best will supplicate, and it will not be answered for you."