23 This did a former Bishop of the Church of Thagasta, Firmus by name, and even more firm in will. For, when he was asked by command of the emperor, through officers sent by him, for a man who was taking refuge with him, and whom he kept in hiding with all possible care, he made answer to their questions, that he could neither tell a lie, nor betray a man; and when he had suffered so many torments of body, (for as yet emperors were not Christian,) he stood firm in his purpose.
Thereupon being brought before the emperor, his conduct appeared so admirable, that he without any difficulty obtained a pardon for the man whom he was trying to save. What conduct could be more brave and constant? But perhaps some more timid person may say, “I can be prepared to bear any torments, or even to submit to death, that I may not sin; but, since it is no sin to tell a lie such that you neither hurt any man, nor bear false witness, and benefit some man, it is foolish and a great sin, voluntarily and to no purpose to submit to torments, and, when one's health and life may haply be useful, to fling them away for nothing to people in a rage.”
Of whom I ask; Why he fears that which is written, “You shall not bear false witness,” and fears not that which is said unto God, “You will destroy all them that speak leasing?” Says he, “It is not written, Every lie: but I understand it as if it were written, You will destroy all that speak false witness.” But neither there is it said, All false witness. “Yes, but it is set there,” says he, “where the other things are set down which are in every sort evil.” What, is this the case with what is set down there, “You shall not kill?” If this be in every sort evil, how shall one clear of this crime even just men, who, upon a law given, have killed many?
“But,” it is rejoined, “that man does not himself kill, who is the minister of some just command.” These men's fear, then, I do accept, that I still think that laudable man who would neither lie, nor betray a man, did both better understand that which is written, and what he understood did bravely put in practice.
Source: On Lying (New Advent)