Contradiction with Jeremiah 31:34
This verse speaks of forgiveness and the erasing of iniquity, contrasting with Psalms 51:8's context of acknowledging sin and seeking restoration.
Jeremiah 31:34: And they shall teach no more every man his neighbour, and every man his brother, saying, Know the LORD: for they shall all know me, from the least of them unto the greatest of them, saith the LORD: for I will forgive their iniquity, and I will remember their sin no more.
Contradiction with 1 John 1:9
Describes forgiveness and cleansing from all unrighteousness through confession, whereas Psalms 51:8 focuses on hearing joy and gladness amidst the context of sin and contrition.
1 John 1:9: If we confess our sins, he is faithful and just to forgive us [our] sins, and to cleanse us from all unrighteousness.