Whoever enjoins good and forbids evil must know what the good and evil are.
Question: Is it obligatory for someone who wants to another person to the good or forbid him from evil to have the power to carry it out?
Answer: Whoever enjoins and forbids must know what the good and evil are and knows that the wrongdoer violates them intentionally and without any shar‘ī excuse. The person exercising the obligation of enjoining good and forbidding evil must be aware of what is good and what is bad, albeit in a general manner.
1. Ayatollah Seyyed Ali Khamenei, Practical Laws of Islam, Q1050.
2. Ayatollah Seyyed Ali Sistani, Jurisprudence Made Easy,Dialogue on enjoining what is good and forbidding what is evil.