Musnad Ahmad 30:3486

Yazid narrated to us, Jahir ibn Yazid al-Abdi informed us, from Khidash ibn Ayyash, who said: I was in a circle in Kufa, when a man was speaking. He said: We were sitting with Abu Hurairah, and he said: I heard the Messenger of Allah, peace and blessings of Allah be upon him, say: "Whoever testifies against a Muslim with a testimony for which he is not worthy, then let him take his seat in the Fire."