This Bible contradiction is from the Skeptic's Annotated Bible.
James and John
Mark 10:35-37 View context
And James and John, the sons of Zebedee, come unto him, saying, Master, we would that thou shouldest do for us whatsoever we shall desire.
And he said unto them, What would ye that I should do for you?
They said unto him, Grant unto us that we may sit, one on thy right hand, and the other on thy left hand, in thy glory.
The mother of James and John
Matthew 20:20-21 View context
Then came to him the mother of Zebedee's children with her sons, worshipping [him], and desiring a certain thing of him.
And he said unto her, What wilt thou? She saith unto him, Grant that these my two sons may sit, the one on thy right hand, and the other on the left, in thy kingdom.