1 Corinthians 8:7

8:7 But this knowledge is not shared by all. And some, by being accustomed to idols in former times, eat this food as an idol sacrifice, and their conscience, because it is weak, is defiled.

Hebrews 9:14

9:14 how much more will the blood of Christ, who through the eternal Spirit offered himself without blemish to God, purify our consciences from dead works to worship the living God.

Hebrews 10:22

10:22 let us draw near with a sincere heart in the assurance that faith brings, because we have had our hearts sprinkled clean from an evil conscience and our bodies washed in pure water.