Full Idea
Everything which is known has number, because otherwise it is impossible for anything to be the object of thought or knowledge.
Gist of Idea
Everything must involve numbers, or it couldn't be thought about or known
Source
Philolaus (On the Cosmos (lost) [c.435 BCE], B04), quoted by John Stobaeus - Anthology 1.21.7b
Book Reference
'The First Philosophers', ed/tr. Waterfield,Robin [OUP 2000], p.111