If I didn't participate in act but I know that act is bad and didn't tell authorities, will I also get gunah?

Question

My brother drinks alcohol and I know it. But I didn't tell my parents and we are less than 18, Will I also get gunah If I don't tell my parents (TBH He told me that he don't have any plans to stop alcohol consumption).

Answer 1

If telling your parents or authorities will have an effect, then it is obligatory on you to do it. This comes under 'Enjoining Good and Forbidding Evil' (الأمر بالمعروف والنهي عن المنكر), and abstaining from it is condemned in the Quran.

لعن الذين كفروا من بني إسرائيل على لسان داوود وعيسى ابن مريم ذلك بما عصوا وكانوا يعتدون كانوا لا يتناهون عن منكر فعلوه لبئس ما كانوا يفعلون

Cursed were those who disbelieved among the Children of Israel by the tongue of David and of Jesus, the son of Mary. That was because they disobeyed and [habitually] transgressed. They used not to prevent one another from wrongdoing that they did. How wretched was that which they were doing.

^{— Quran 5:78}

لولا ينهاهم الربانيون والأحبار عن قولهم الإثم وأكلهم السحت لبئس ما كانوا يصنعون

Why do the rabbis and religious scholars not forbid them from saying what is sinful and devouring what is unlawful? How wretched is what they have been practicing.

^{— Quran 5:63}

من رأى منكم منكرا فليغيره بيده فإن لم يستطع فبلسانه فإن لم يستطع فبقلبه وذلك أضعف الإيمان

Whoever among you sees an evil action, let him change it with his hand; if he cannot, then with his tongue; and if he cannot, then (only detest it) with his heart and that is the weakest of faith.

^{— Muslim}

Also see 3:104, 3:110, 3:114, 5:63 7:165, 9:71, 9:112, 22:41, 31:17 etc.