This Bible contradiction is from the Skeptic's Annotated Bible.
700 men in chariots and 40,000 horsemen
2 Samuel 10:18 View context
And the Syrians fled before Israel; and David slew [the men of] seven hundred chariots of the Syrians, and forty thousand horsemen, and smote Shobach the captain of their host, who died there.
7000 men in chariots and 40,000 footmen
1 Chronicles 19:18 View context
But the Syrians fled before Israel; and David slew of the Syrians seven thousand [men which fought in] chariots, and forty thousand footmen, and killed Shophach the captain of the host.