Aristotle: Virtue Proves the Existence of God

"The question might be raised 'Is luck the cause of this very thing--desiring what one should or when one should?' Or will luck in that way be the cause of everything? For it will be the cause both of thinking and deliberating; for a man who deliberates has not deliberated already before deliberating and deliberated also about that--there is some starting point. Nor did he think, after thinking already before thinking, and so on to infinity. Intelligence, therefore, is not the starting point of thinking, nor is counsel the starting point of deliberation. So what else is there save luck? Thus everything will be by luck. Or is there some starting-point beyond which there is not other, and this-because it is of such a sort--can have such an effect? But what is being sought is this: What is the starting point of change in the soul? It is now evident: as it is a god that moves in the whole universe, so it is in the soul; for in a sense, the divine element in us moves everything; but the starting-point of reason is not reason but something superior. What then could be superior to knowledge and intelligence but a god? For virtue is an instrument of intelligence."

Aristotle, Eudemian Ethics, Book VIII.