Musnad Ahmad 489:9

Yunus narrated to us, Shaiban narrated to us, from Qatadah, who said: Mutarrif narrated from Iyad ibn Himar, that he asked the Prophet, peace and blessings of Allah be upon him, and said: "O Messenger of Allah, what is your opinion of a man who insults me while he is of lower lineage than me?" The Messenger of Allah, peace and blessings of Allah be upon him, said: "The two who insult one another are two devils; they disparage one another and call one another liars."