Origen

“ For these are the things which defile the man, when they come forth out of the heart, and going out from it proceed through the mouth; so that, if they did not come out of the heart, but were retained there somewhere about the heart, and were not allowed to be spoken through the mouth, they would very quickly disappear, and a man would be no more defiled. The spring and source, then, of every sin are evil thoughts; for, unless these gained the mastery, neither murders nor adulteries nor any other such thing would exist. Therefore, each man must keep his own heart with all watchfulness ”

“ We have thus investigated according to our ability what are the things which defile; but to eat with unwashed hands does not defile the man; but if we must say it with boldness, with unwashed heart to eat anything whatsoever which is the natural food of our reason, defileth the man. ”

“ And if we seem to some to have made a digression in speaking of these things, consider if it were not necessary that they should be said, because that evil thoughts are the spring of all sins, and can pollute even those actions which, if they were done apart from evil thoughts, would have justified the man who did them. ”