Full Idea
The 'golden rule' is merely derivative from our principle, but it cannot be a universal law since it isn't the ground of duties to oneself or others (since it implies a breakable contract).
Gist of Idea
The 'golden rule' cannot be a universal law as it implies no duties
Source
Immanuel Kant (Groundwork of the Metaphysic of Morals [1785], 430.68 n)
Book Reference
Kant,Immanuel: 'The Moral Law (Groundwork of Morals)', ed/tr. Paton,H.J. [Hutchinson 1948], p.92