Full Idea
To have recourse to God in explaining the arrangements of nature is not a physical explanation but a confession that one has come to the end of philosophy, since one assumes something of which one has no concept to conceive what is before one's eyes.
Gist of Idea
Using God to explain nature is referring to something inconceivable to explain what is in front of you
Source
Immanuel Kant (Critique of Practical Reason [1788], I.II.II.VI)
Book Reference
Kant,Immanuel: 'Critique of Practical Reason (Third edition)', ed/tr. Beck,Lewis White [Library of Liberal Arts 1993], p.145
A Reaction
Hume had many objections to the design argument, some of them positively sarcastic, but none as ruthless as this, since Kant (here) seems to find God to be a totally empty concept, and hence a complete non-starter as explanation for anything.