Full Idea
Not only do the objects of knowledge owe their being known to the good, but their being is also due to it, although the good is not being, but superior to it in rank and power.
Gist of Idea
Being depends on the Good, which is not itself being, but superior to being
Source
Plato (The Republic [c.371 BCE], 509b)
Book Reference
Plato: 'Complete Works', ed/tr. Cooper,John M. [Hackett 1997], p.1130
A Reaction
I was surprised to find that in Plotinus the One is not being, because it is the source of being, and thus superior to being. Then a footnote sent me here, and I realise that Plato thought that the Form of the Good is superior to Being.