Musnad Ahmad 652:53

'Abd al-Razzaq narrated to us, Isra'il informed us, from Simak ibn Harb, that he heard al-Nu'man ibn Bashir saying: The Messenger of Allah (peace and blessings of Allah be upon him) said: "I have warned you of the Fire, I have warned you of the Fire." [He continued repeating it] until, if a man had been at the furthest end of the market, he would have heard him, and the people of the market heard his voice, while he was upon the pulpit.