Musnad Ahmad 30:1537

Aswad ibn Amir narrated to us, he said: Jarir ibn Hazim narrated to us, from al-Hasan, from Abu Hurayrah, he said: The Messenger of Allah, peace and blessings of Allah be upon him, said: "Indeed, a man speaks a word, not thinking that it will reach where it reached, [but] he falls by it into the Fire [for] seventy autumns."