Once a Yogini called Sulabha came to test King Janaka. Though old and weak she disguised herself as a beautiful and charming lady, with her yogic power. Janaka received her and treated her with great respect. But she tried to attract Janaka with her beauty. She behaved in amorous ways.
Janaka enquired about her whereabouts and told her that he was the disciple of Rishi Panchasikha and has renounced all the materialistic pleasures, for him gold is equal to sand and added that knowledge is more important to attain moksha (salvation) but not lust and wealth. He further said that it was not right on her part to behave that way.
On hearing his words, Sulabha told him that she belonged to a great lineage and received knowledge and wisdom from Mahatmas. She had come all the way in search of a husband and having heard about Janaka, that he had attained liberation, came to him to propose marriage but was disappointed.
Janaka remained calm with a genuine smile on his face.
Sulabha said that it was indeed foolish to test whether he had really attained liberation. It was as if to test whether fire is hot. Then she spent some time in the spiritual discourses in his court and left the place satisfied.
According to the great poet Kalidasa a real hero is a person who doesn't get distracted by any kind of desires. So, this incident reveals Janaka's true heroism.
Source - Srinivasa Bala Bharati – 125 (Children Series) – Janaka English Translation Prof. K. V. Ramakrishnamacharyulu