Proverbs 4:23 (KJV)
Keep thy heart with all diligence; for out of it are the issues of life.
Matthew 12:34 (KJV)
O generation of vipers, how can ye, being evil, speak good things? for out of the abundance of the heart the mouth speaketh.
Acts 24:16 (KJV)
And herein do I exercise myself, to have always a conscience void to offence toward God, and toward men.