Do not let your deeds belie your words, lest when you speak in church someone may say to himself, “Why do you not practice what you preach?”

Jerome of Stridon (c. 347-420) Roman Christian priest, theologian, historian, translator, Doctor of the Church [Saint Jerome, Eusebius Sophronius Hieronymus, Εὐσέβιος Σωφρόνιος Ἱερώνυμος]

Letter 52, to Nepotian (AD 394)

Alt. trans.: "Do not let your deeds belie your words; lest when you speak in church someone may mentally reply, 'Why do you not practice what you profess?'" [Philip Schaff & Henry Wace (eds.) A Select Library of Nicene and Post-Nicene Fathers of the Christian Church, vol. 6 (1893)]