Here are 4 Bible verses about purity of heart from the Old and New Testaments of the Holy Bible (King James Version), sorted from most to least relevant.
James 4:8 KJV
Draw nigh to God, and he will draw nigh to you. Cleanse your hands, ye sinners; and purify your hearts, ye double minded.
1 Timothy 5:22 KJV
Lay hands suddenly on no man, neither be partaker of other men’s sins: keep thyself pure.
2 Corinthians 7:1 KJV
Having therefore these promises, dearly beloved, let us cleanse ourselves from all filthiness of the flesh and spirit, perfecting holiness in the fear of God.
Matthew 5:8 KJV
Blessed are the pure in heart: for they shall see God.