Hercule et Omphale
The Lydian queen Omphale actually owned Hercules, as a slave. She bought the hero from the god Hermes, who sold him following an oracle which declared that Hercules must be sold into slavery for three years.
Hercules had sought the oracle to find out what he had to do in order to purify himself, after he murdered his friend Iphitus and stole the Delphic tripod.