Where does C. S. Lewis teach that a virtuous attitude can be developed by acting virtuously?

I recall reading something by C. S. Lewis some time ago in which he recommends that a person who wants to develop a virtuous, right attitude in some area of life should begin acting virtuously in that realm, even though his attitude is wrong. After a time, Lewis says, the virtuous actions will lead to the development of a virtuous attitude. Recently this struck me as a particularly Aristotelian approach to moral development . One introductory textbook relates Aristotle's view this way: > We should perform acts that resemble virtuous acts, that resemble what we would do if we had the disposition. In this way we build up the right habits. If the disposition I wish to acquire is liberality, the way to acquire it is to ask how I would behave if I possessed the habit and continue to behave that way. (Ronald Nash , *Life's Ultimate Questions *, p. 152 ) I'd like to explore how this idea might fit in the framework of sanctification, but unfortunately I don't remember where I read it. Where in the works of C. S. Lewis does he teach that a virtuous attitude can be developed by acting virtuously?