Full Idea
I never asserted so absurd a proposition as that anything might arise without a cause: I only maintained that our certainty of the falsehood of that proposition proceeded neither from intuition nor from demonstration, but from another source.
Gist of Idea
That events could be uncaused is absurd; I only say intuition and demonstration don't show this
Source
David Hume (Letters [1739], 1754), quoted by Brian Davies - Introduction to the Philosophy of Religion 5 'God'
Book Reference
Davies,Brian: 'An Introduction to the Philosophy of Religion' [OUP 1993], p.77
A Reaction
Since the other source is habit, he is being a bit disingenuous. While rational intuition and demonstration give a fairly secure basis for the universality of causation, mere human habits of expectation give very feeble grounds.