This Bible contradiction is from the Infidels.org.
Matthew 12:30 View context
He that is not with me is against me; and he that gathereth not with me scattereth abroad.
Mark 9:40 View context
For he that is not against us is on our part.
Luke 9:50 View context
And Jesus said unto him, Forbid [him] not: for he that is not against us is for us.