The Obligation of Commanding the Good and Forbidding the Evil

The believers, men and women are Auliya (helpers, supporters, friends and protectors) of one another, they enjoin (on the people) Al-Ma'ruf (i.e. Islamic Monotheism and all that Islam orders one to do) and forbid people from Al-Munkar (i.e. polytheism and disbelief of all kinds, and all that Islam has forbidden); they preform As-Salat (Iqamat-as-Salat) and give the Zakat and obey Allah and His Messenger. Allah will have his Messenger. Allah will have His Mercy on them. Surely Allah is All-Mighty, All-Wise.

(Surah At-Tawbah:71)