keeping a clear conscience, so that those who slander you may be put to shame by your good behavior in Christ.
KJV
Having a good conscience; that, whereas they speak evil of you, as of evildoers, they may be ashamed that falsely accuse your good conversation in Christ.
ASV
having a good conscience; that, wherein ye are spoken against, they may be put to shame who revile your good manner of life in Christ.