Full Idea
Existence is not a perfection in God or in anything else; it is that without which no perfections can be present.
Gist of Idea
Existence is not a perfection; it is what makes perfection possible
Source
comment on René Descartes (Meditations [1641], §5.67) by Pierre Gassendi - Objections to 'Meditations' (Fifth) 323
Book Reference
Descartes,René: 'Meditations on First Philosophy etc.', ed/tr. Cottingham,John [CUP 1986], p.96