For Quintus Roscius the Actor (47)

But I, on the contrary, argue in this way. The authority of Cluvius would be less if be were speaking on his oath, than it is now when he is not speaking on his oath. For then, perhaps, he might seem to bad men over eager in being a witness in a cause in which he had been judge. But now he must appear to all his enemies most upright and most wise, inasmuch as he only tells his intimate friends what he knows.