Listen to Me, all of you, and understand: there is nothing outside the man which going into him can defile him; but the things which proceed out of the man are what defile the man. (Mark 7:14-15).
“Do you not understand that whatever goes into the man from outside cannot defile him; because it does not go into his heart, but into his stomach, and is eliminated?” (Thus He declared all foods clean.) And He was saying, “That which proceeds out of the man, that is what defiles the man. For from within, out of the heart of men, proceed the evil thoughts, fornications, thefts, murders, adulteries, deeds of coveting and wickedness, as well as deceit, sensuality, envy, slander, pride and foolishness. All these evil things proceed from within and defile the man.” (Mark 7:18-23).
For the mouth speaks out of that which fills the heart. The good man out of his good treasure brings forth what is good; and the evil man out of his evil treasure brings forth what is evil. (Matthew 12:34-35).
See also 1 Timothy 4:3-5.