Full Idea
No thing comes into being or passes away, but it is mixed together or separated from existing things. Thus it would be correct if coming into being was called 'mixing', and passing away 'separation-off''.
Gist of Idea
Nothing is created or destroyed; there is only mixing and separation
Source
Anaxagoras (fragments/reports [c.460 BCE], B17), quoted by Simplicius - On Aristotle's 'Physics' 163.20
Book Reference
'Ancilla to the Pre-Socratic Philosophers', ed/tr. Freeman,Kathleen [Harvard 1957], p.85
A Reaction
I take this to be the first axiom of the new subject of chemistry. Our world is just patterns of Being. The bigger puzzle is - why those patterns?