Mediator Dei §181

¹⁸¹ Any inspiration to follow and practice extraordinary exercises of piety must most certainly come from the Father of Lights, from whom every good and perfect gift descends; and, of course, the criterion of this will be the effectiveness of these exercises in making the divine cult loved and spread daily ever more widely, and in making the faithful approach the sacraments with more longing desire, and in obtaining for all things holy due respect and honor. If on the contrary, they are an obstacle to principles and norms of divine worship, or if they oppose or hinder them, one must surely conclude that they are not in keeping with prudence and enlightened zeal.