Full Idea
Since every basic truth depends on God's omnipotence, I would not dare to say that God cannot make it....that one and two should not be three.
Gist of Idea
It is possible that an omnipotent God might make one and two fail to equal three
Source
René Descartes (Letters to Antoine Arnauld [1645]), quoted by A.W. Moore - The Evolution of Modern Metaphysics 01.3
Book Reference
Moore,A.W.: 'The Evolution of Modern Metaphysics' [CUP 2013], p.33
A Reaction
An unusual view. Most people would say that if Descartes can doubt something that simple, he should also doubt his reasons for believing in God's existence.