Musnad Ahmad 1043:1

Hassan narrated to us, Ibn Lahi'ah narrated to us, Yazid ibn 'Amr al-Mu'afiri narrated to us, from a man from Banu Ghifar, that the Messenger of Allah (may Allah bless him and grant him peace) said: "Whoever does not shave his pubic hair, trim his nails, and clip his mustache is not of us."