This Bible contradiction is from the Infidels.org.
Matthew 5:1 View context
And seeing the multitudes, he went up into a mountain: and when he was set, his disciples came unto him:
Luke 6:17 View context
And he came down with them, and stood in the plain, and the company of his disciples, and a great multitude of people out of all Judaea and Jerusalem, and from the sea coast of Tyre and Sidon, which came to hear him, and to be healed of their diseases;