The Six Books of Proclus on the Theology of Plato, Volume 2

For if it should be corrupted, it would desert itself, and would be without itself. This however is impossible. For being one thing, it is at the same time cause and the thing caused. But every thing which is corrupted, departing from the cause of itself is corrupted. For so far as it adheres to that which contains, connects and preserves it, it is connected and preserved. But that which is self-subsistent never leaves its cause, because it does not desert itself; for it is the cause of itself. Every thing therefore self-subsistent is incorruptible.