John Chrysostom
Catena Aurea · Lukasevangelium 6
For a good tree bringeth not forth corrupt fruit; neither doth a corrupt tree bring forth good fruit. For every tree is known by his own fruit. For of thorns men do not gather figs, nor of a bramble bush gather they grapes. A good man out of the good treasure of his heart bringeth forth that which is good; and an evil man out of the evil treasure of his heart bringeth forth that which is evil: for of the abundance of the heart his mouth speaketh.
(Hom. 42. in Matt.) For it is a natural consequence when wickedness abounds within, that wicked words are breathed as far as the mouth; and therefore when you hear of a man uttering abominable things, do not suppose that there lies only so much wickedness in him as is expressed in his words, but believe the fountain to be more copious than the stream.