16 Or, are some lies, also, to be excepted, so that it were better to suffer this than to commit those? If so, then not every thing that is done in order to the avoiding of that defilement ceases to be sin; seeing there are some lies to commit which is worse than to suffer that foul violence. For, suppose quest be making after a person that his body may be deflowered, and that it be possible to screen him by a lie; who dares to say that even in such a case a lie ought not be told?
But, if the lie by which he may be concealed be one which may hurt the fair fame of another, by bringing upon him a false accusation of that very uncleanness, to suffer which the other is sought after; as, if it should be said to the inquirer, “Go to such an one,” (naming some chaste man who is a stranger to vices of this kind,) “and he will procure for you one whom you will find a more willing subject, for he knows and loves such;” and thereby the person might be diverted from him whom he sought: I know not whether one man's fair fame ought to be violated by a lie, in order that another's body may not be violated by lust to which he is a stranger.
And in general, it is never right to tell a lie for any man, such as may hurt another, even if the hurt be slighter than would be the hurt to him unless such a lie were told. Because neither must another man's bread be taken from him against his will, though he be in good health, and it is to feed one who is weak; nor must an innocent man, against his will, be beaten with rods, that another may not be killed. Of course, if they are willing, let it be done, because they are not hurt if they be willing that so it should be: but whether, even with his own consent, a man's fair fame ought to be hurt with a false charge of foul lusts, in order that lust may be averted from another's body, is a great question.
And I know not whether it be easy to find in what way it can be just that a man's fair fame, even with his consent, should be stained with a false charge of lust, any more than a man's body should be polluted by the lust itself against his will.
Source: On Lying (New Advent)