Full Idea
Pythagoreans said that entities existed by imitation of the numbers, whereas Plato said that it was by participation.
Gist of Idea
Pythagoreans say things imitate numbers, but Plato says things participate in numbers
Source
report of Pythagoras (reports [c.530 BCE]) by Aristotle - Metaphysics 987b
Book Reference
Aristotle: 'Metaphysics', ed/tr. Lawson-Tancred,Hugh [Penguin 1998], p.24