>15. And as for that saying of the Apostle, “Putting away lying, speak every man truth with his neighbor, for we are members one of another,” far be it that we should so understand it, as though he had permitted to speak a lie with those who are not yet with us members of the body of Christ. But the reason why it is said, is, because each one of us ought to account every man to be that which he wishes him to become, although he be not yet become such; as the Lord showed the alien Samaritan to be neighbor to him unto whom he showed mercy.” A neighbor then, and not an alien, is that man to be accounted, with whom our concern is that he remain not an alien; and if on the score of his not being yet made partaker of our Faith and Sacrament, there be some truths that must be concealed from him, yet is that no reason why false things should be told him.
Reproduced in full. Translation: Nicene and Post-Nicene Fathers, series 1, vol. 3 (Schaff, 1887), public domain (Public domain).