A musician would not willingly consent that his lyre should be out of tune, nor a leader of a chorus that his chorus should not sing in the strictest possible harmony; but shall each individual person be at variance with himself, and shall he exhibit a life not at all in agreement with his words?

[εἶτα μουσικὸς μὲν οὐκ ἂν ἑκὼν δέξαιτο ἀνάρμοστον αὐτῷ τὴν λύραν εἶναι, καὶ χοροῦ κορυφαῖος μὴ ὅτι μάλιστα συνᾷάδοντα τὸν χορὸν ἔχειν” αὐτὸς δέ τίς ἕκαστος διαστασιάσει πρὸς ἑαυτόν, καὶ οὐχὶ τοῖς λόγοις ὁμολογοῦντα τὸν βίον παρέξεται.]

basil the great
Basil of Caesarea (AD 330-378) Christian bishop, theologian, monasticist, Doctor of the Church [Saint Basil the Great, Ἅγιος Βασίλειος ὁ Μέγας]
Address to Young Men on Reading Greek Literature, ch. 6, sec. 3 [tr. Deferrari/McGuire (1933)]
    (Source)