Buford was being audited by the IRS.

He figured that even if his son, brother in-law and his half-uncle were the same person, he should still be able to claim three dependents.

The poor IRS auditor was so flustered that he gave Buford the opportunity to plead his case with a single statement.

If the statement was true, Buford would be fined $10,000. If the statement was false, 'ol Buford would rot in prison for 10 years.

What did Buford say that got the auditor to dismiss the charges altogether?

Buford said to the auditor, "I will rot in prison for 10 years."

If that statement were true, Buford would NOT rot in prison, he would be fined $10,000.
Thus, it can't be true.

The statement can't be false either, because the penalty would be that Buford would rot in prison for 10 years.