Full Idea
I can indeed will to lie, but I can by no means will a universal law of lying; for by such a law there could properly be no promises at all.
Gist of Idea
If lying were the universal law it would make promises impossible
Source
Immanuel Kant (Groundwork of the Metaphysic of Morals [1785], 403.19)
Book Reference
Kant,Immanuel: 'The Moral Law (Groundwork of Morals)', ed/tr. Paton,H.J. [Hutchinson 1948], p.68