66 What is asserted in favor of the social and eugenic "indication" may and must be accepted, provided lawful and upright methods are employed within the proper limits; but to wish to put forward reasons based upon them for the killing of the innocent is unthinkable and contrary to the divine precept promulgated in the words of the Apostle: Evil is not to be done that good may come of it.
Source: Casti Connubii (Vatican.va)