One day a youth approached the Noble Prophet (s.a.w) and with utmost disrespect and discourtesy, said: “O’ Prophet of Allah! Do you permit me to commit fornication?”
These words created a great uproar amongst the people and objections could be heard from every nook and corner. The Noble Prophet (s.a.w), exhibiting sublime ethics and speaking with absolute gentleness, said: “Come near.” The youth stepped forward and sat down beside him (s.a.w), whereupon the Prophet asked: “Would you like someone to commit the act with your mother?” The youth replied: “May I be made your ransom! Never.” The Noble Prophet (s.a.w) said: “Similarly the (other) people too do not approve of this with respect to their daughters.”
The Noble Prophet (s.a.w) continued: “Tell me: Would you approve of this act for your sister?” Once again the youth denied (and repented having asked the question).
The Noble Prophet (s.a.w) placed his hands upon the youth’s chest and prayed for him, saying: “O’ Lord! Purify his heart, forgive his sins and protect him from the pollution of depravity.” From then onwards fornication became the worst of the deeds in the eyes of the youth.( Dastan-ha Wa Pand-ha, vol. 3, pg. 138; Tafsir al-Manar, under the discussion related to verse 104 of Surat Ale ‘Imran )