Full Idea
How could a thing exist, no part of which ever exists? In the case of time, nothing exists but instants, and an instant is not even a part of time.
Gist of Idea
No time exists except instants, and instants are not even a part of time, so time does not exist
Source
Gottfried Leibniz (Letters to Samuel Clarke [1716], 5.49)
Book Reference
Leibniz,Gottfried: 'Philosophical Writings', ed/tr. Parkinson,G.H.R. [Dent 1973], p.233