This Bible contradiction is from the Skeptic's Annotated Bible.
Exodus 19:20 View context
And the LORD came down upon mount Sinai, on the top of the mount: and the LORD called Moses [up] to the top of the mount; and Moses went up.
Exodus 20:22 View context
And the LORD said unto Moses, Thus thou shalt say unto the children of Israel, Ye have seen that I have talked with you from heaven.
Galatians 3:19 View context
Wherefore then [serveth] the law? It was added because of transgressions, till the seed should come to whom the promise was made; [and it was] ordained by angels in the hand of a mediator.