Full Idea
The human intellect is not capable of conceiving of infinity, and hence it neither has nor can contemplate any idea representing an infinite thing.
Gist of Idea
We can never conceive of an infinite being
Source
comment on René Descartes (Meditations [1641], §5.65) by Pierre Gassendi - Objections to 'Meditations' (Fifth) 286
Book Reference
Descartes,René: 'Meditations on First Philosophy etc.', ed/tr. Cottingham,John [CUP 1986], p.81