Ubayy bin Ka'b (may Allah be pleased with him) narrates: I heard the Messenger of Allah (peace and blessings be upon him) say: "Whoever ascribes himself to the lineage of the days of ignorance (and boasts about it), tell him to bite his father's private part and do not say this as a euphemism." Chain is weak. Narrated in Sharh al-Sunnah, Ahmad, and al-Bukhari in al-Adab al-Mufrad.