Full Idea
In the case of God necessary existence is in fact a property in the strictest sense of the term, since it applies to him alone and forms a part of his essence as it does of no other thing
Gist of Idea
Necessary existence is a property which is uniquely part of God's essence
Source
René Descartes (Reply to Fifth Objections [1641], 383)
Book Reference
Descartes,René: 'Meditations on First Philosophy etc.', ed/tr. Cottingham,John [CUP 1986], p.97