1
general::
Phrase(s): have a clear conscience (about someone or something) [and] have a clean conscience (about someone or something)
to be free of guilt about someone or something. • I’m sorry that John got the blame. I have a clean conscience about the whole affair. • I have a clear conscience about John and his problems. • I didn’t do it. I swear to that with a clean conscience.
McGrawhill's American Idioms And Phrasal Verbs
2
general::
Also, have a clean conscience. Feel free of guilt or responsibility. For example, I have a clear conscience? I did all I could to help. This idiom is Also put as one's conscience is clear or clean, as in His conscience is clean about telling the whole story. The adjective clear has been used in the sense of "innocent" since about 1400; clean was so used from about 1300.
American Heritage Idioms