Hadith 37:74
Waki’ narrated to us, from Kahmas, from al-Hasan, from Ubayy ibn Ka’b, who said: I heard the Messenger of Allah, may Allah bless him and grant him peace, say: "Whoever affiliates himself with tribes, then bite him with his father’s private parts, and do not use euphemisms."
حدثنا وكيع عن كهمس عن الحسن عن أبي بن كعب قال سمعت رسول الله صلى الله عليه وسلم يقول من اتصل بالقبائل فاعضوه بهن أبيه ولا تكنوا