Full Idea
In the Prolegomena to his work there is a famous statement that moral principles laid down in the work would have some degree of validity even if there was no God commanding obedience.
Gist of Idea
Moral principles have some validity without a God commanding obedience
Source
report of Hugo Grotius (On the Law of War and Peace [1625]) by Thomas Mautner - Penguin Dictionary of Philosophy p.229
Book Reference
Mautner,Thomas: 'Dictionary of Philosophy' [Penguin 1997], p.229
A Reaction
I am not clear why Grotius felt obliged to qualify his claim with the phrase 'some degree'. I don't see how God's command can affect the 'validity' of morality, or how there can be a middle ground between dependence on and independence of God.