Reference for Ketubot 102:17

ת"ר שבויי מלכות הרי הן כשבויין גנובי ליסטות אינן כשבויין והתניא איפכא

Our rabbis taught: Royal captives have the status of ordinary captives but those that are kidnapped by highwaymen are not regarded as ordinary captives. But have we not taught the reverse!?

Jastrow