Musnad Ahmad 962:175

Husayn ibn Muhammad and others narrated to us, they said: Muhammad ibn Mutarrif narrated to us, from Hassan ibn Atiyyah, from Abu Umamah al-Bahili, from the Prophet, peace and blessings of Allah be upon him, who said: "Modesty and reticence are two branches of faith, and obscenity and eloquence [in a blameworthy sense] are two branches of hypocrisy."