Full Idea
That which is in opposition is in concert, and from things that differ comes the beautiful harmony.
Clarification
'In concert' means harmonious
Gist of Idea
Beautiful harmony comes from things that are in opposition to one another
Source
Heraclitus (fragments/reports [c.500 BCE], B008), quoted by Aristotle - Nicomachean Ethics 1155b04
Book Reference
'Ancilla to the Pre-Socratic Philosophers', ed/tr. Freeman,Kathleen [Harvard 1957], p.25