Nicene and Post-Nicene Fathers, Ser. II, Vol. XII:
The Book of Pastoral Rule, and Selected Epistles, of Gregory the Great.: Of the work and the voice of preaching.

But in the midst of these things we are brought back by the earnest desire of charity to what we have already said above; that every preacher should give forth a sound more by his deeds than by his words, and rather by good living imprint footsteps for men to follow than by speaking shew them the way to walk in.  For that cock, too, whom the Lord in his manner of speech takes to represent a good preacher, when he is now preparing to crow, first shakes his wings, and by smiting himself makes himself more awake; since it is surely necessary that those who give utterance to words of holy preaching should first be well awake in earnestness of good living, lest they rouse others with their voice while themselves torpid in performance; that they should first shake themselves up by lofty deeds, and then make others solicitous for good living; that they should first smite themselves with the wings of their thoughts; that whatsoever in themselves is unprofitably torpid they should discover by anxious investigation, and correct by strict animadversion, and then at length set in order the life of others by speaking; that they should take heed to punish their own faults by bewailings, and then denounce what calls for punishment in others; and that, before they give voice to words of exhortation, they should proclaim in their deeds all that they are about to speak.