This Bible contradiction is from the Skeptic's Annotated Bible.
Verses
Joel.
1 Samuel 8:2 View context
Now the name of his firstborn was Joel; and the name of his second, Abiah: [they were] judges in Beer-sheba.
Vashni.
1 Chronicles 6:28 View context
And the sons of Samuel; the firstborn Vashni, and Abiah.