Full Idea
Since the one is everywhere alike, then if it is divisible, it will be equally divisible everywhere….so let it be divided everywhere. It is obvious that nothing will remain and the whole will vanish, and so (if it is compound) it is composed of nothing.
Gist of Idea
The one can't be divisible, because if it was it could be infinitely divided down to nothing
Source
report of Parmenides (fragments/reports [c.474 BCE]) by Simplicius - On Aristotle's 'Physics' 9.139.5-
Book Reference
'The First Philosophers', ed/tr. Waterfield,Robin [OUP 2000], p.78
A Reaction
he is quoting Porphyry