Full Idea
No one thing among things subject to change can possibly be exactly like any other thing, without becoming the same thing.
Gist of Idea
Each thing must be in some way unique
Source
Diogenes (Apoll) (fragments/reports [c.440 BCE], B05), quoted by Simplicius - On Aristotle's 'Physics' 153.8
Book Reference
'Ancilla to the Pre-Socratic Philosophers', ed/tr. Freeman,Kathleen [Harvard 1957], p.88
A Reaction
This is said to be the first ever formulation of the principle of identity of indiscernible.