Volume 1. 3rd Topic. Q 7

“Proof that God is perfectly simple.

IV. This proved to be a property of God: (1) from his independence, because composition is of the formal reason of a being originated and dependent  (since nothing can be composed by itself ,  but whatever is composed  must necessarily be composed by another; now God is the first and independent being, recognizing no other prior to himself) ; (2) from his unity, because he who is absolutely one, is also absolutely simple and therefore can neither be dived nor composed; (3) from his perfection, because composition implies imperfection inasmuch as it supposes passive power, dependency and mutability. ”

Institutes of Elenctic Theology Volume 1 (P & R Publishing: Phillipsburg, NJ, 1992), pg. 191

So does he give us scripture for this assertion? Where then does he get it from? Neo-Platonism and the Parmenidean One. See my video here.