Or when our Lord says, The truth is not in him, He intends it as an index: as if we had asked Him, how it appeared that the devil stood not in the truth; and He said, Because the truth is not in him. For it would be in him, if he stood in it.
When he speaketh a lie, he speaketh of his own: for he is a liar, and the father of it.
Reproduced in full. Translation: Oxford 1841 (Newman), public domain (Public domain).
Also cites: xi. de Civ. Dei, c. xiv