Sahih Muslim Book 32, Hadith Number 6196.

Nawwis b. Sim’in reported: I stayed with Allah’s Messenger (may peace be upon him) for one year. What obstructed me to migrate was (nothing) but (persistent) inquiries from him (about Islam). (It was a common observation) that when anyone of us migrated (to Medina) he ceased to ask (too many questions) from Allah’s Messenger (may peace be upon him). So I asked him about virtue and vice. Thereupon Allah’s Messenger (may peace be upon him) said: Virtue is a kind disposition and vice is what rankles in your mind and that you disapprove of its being known to the people.