During one of my exams the invigilator allowed full, complete cheating in the classroom. I did not cheat even one word. However I felt that cheating being allowed was unfair, because due to the noise of students asking each other questions, my exam did not go well due to noise. Feeling that something unfair had been done, I immediately filed a complaint against the invigilator with the headmistress, and from then on she was always sent with another invigilator. But i remember a hadith in which it is said that if you hide other people's faults, Allah will hide your faults on the day of judgement. I also remember my Islamic Studies teacher telling us that if we spotted someone doing wrong, we were first to convince him to stop and if he didnt then complain publicly.. As I did not know her well I couldn't ask her to stop. So was my complaint to the headmistress permissible? What would have been more virtuous in this case? I also feel it is important to mention that later I found out that this was not the first time of her allowing students to cheat, but it was the first time someone had actually helped the headmistress to get to the truth.

All perfect praise be to Allaah, The Lord of the Worlds. I testify that there is none worthy of worship except Allaah, and that Muhammad is His slave and Messenger.

There is nothing wrong with you reporting the incident to the headmistress in order to put an end to that evident forbidden act. It would have been better for you to advise the invigilator first and warn her that you would report her to the headmistress. If she did not listen to you, then you could report her in order to prevent her from doing evil and change a situation that involves a sin. Cheating is certainly prohibited and incurs grave evils. That is why the Prophet said: “Whoever cheats us is not one of us.” [Muslim]

Allaah Knows best.