Bava Batra 34 - The Case of the Silver Ingot of Rav Abba
A certain man snatched a silver ingot from his fellow. There was one witness to the snatching, but the defendant said, "Yes, I snatched it, but it was my ingot that I snatched!"
Rabbi Ami considered the case:
* Should he be required to pay? But there aren't two witnesses!
* Exempt him based on "Why would he lie?" - he could deny having snatched it altogether? This argument is weakened by the witness.
* Make him swear that he did not snatch it? But he himself admits that he did!
* Make him swear that the ingot was his? We can't concoct oaths!
Rav Abba offered a solution. The snatcher is obligated to take an oath but can not do so, and all such people must pay.