This Bible contradiction is from the Skeptic's Annotated Bible.
John 5:31 View context
If I bear witness of myself, my witness is not true.
John 8:14 View context
Jesus answered and said unto them, Though I bear record of myself, [yet] my record is true: for I know whence I came, and whither I go; but ye cannot tell whence I come, and whither I go.