Full Idea
The universal imperative may also run as follows: 'Act as if the maxim of your action were to become through your will a universal law of nature'.
Gist of Idea
Act as if your maxim were to become a universal law of nature
Source
Immanuel Kant (Groundwork of the Metaphysic of Morals [1785], 421.52)
Book Reference
Kant,Immanuel: 'The Moral Law (Groundwork of Morals)', ed/tr. Paton,H.J. [Hutchinson 1948], p.84