Is it obligatory for one who has learned a religious or worldly science to teach it?

Teaching knowledge is among the communal obligations (Fard Kifayah); there must be someone to teach people matters of their religion and their worldly life. And teaching may become an individual obligation (Fard Ayn) upon one who possesses knowledge that no one else knows, or upon whom people ask about what is permissible or forbidden, due to the Almighty’s saying: (And [mention, O Muhammad], when Allah took a covenant from those who were given the Scripture, [saying], "You must make it clear to the people and not conceal it.") [Quran 3:187], and due to the Hadith: "Whoever is asked about knowledge and conceals it will be bridled with a bridle of fire on the Day of Resurrection." Some cases are exempted from this, such as fear of discord (fitna).