From the opening of Book (Chapter) II of the Nicomachean Ethics:



"Excellence, then, being of two kinds, intellectual and moral, intellectual excellence in the main owes both its birth and its growth to teaching (for which reason it requires experience and time), while moral excellence comes about as a result of habit."



Plus reflections on the practical approach of Aristotle in general, and the positive outlook that how what you do becomes ones habits (and who you are), and good habits over time will build and constitute ones character.