Musnad Ahmad 1007:22

Muhammad ibn Ubayd narrated to us, Muhammad—meaning Ibn Ishaq—narrated to us, the son of Ka’b ibn Malik narrated to me, from Abu Qatadah, who said: I heard the Messenger of Allah (peace and blessings of Allah be upon him) saying upon this pulpit: "O people, beware of speaking too much about me. Whoever speaks about me, let him not say anything except the truth or the veracious. For whoever says about me what I have not said, let him take his seat in the Fire."