Hilary of Poitiers - On The Trinity : Book 3 - c. 360 AD

Hilary of Poitiers / Hilarius Pictaviensis / Malleus Arianorum
DE TRINITATE
LIBER III
"...the third book makes further progress, sure though slow. Citing the greatest instances of His power, it brings within the range of faith's understanding that saying, in itself beyond our comprehension, I in the Father and the Father in Me (John 10:38), which Christ utters concerning Himself. "