Hadith: Anyone of you who sees something evil should change it.

عن أبي سعيد الخدري رضي الله عنه قال: سمعت رسول الله صلى الله عليه وآله وسلم يقول: «من رأى منكم منكراً فليُغيِّره بيده، فإلم يستطع فبلسانه، فإلم يستطع فبقلبه، وذلك أضعف الإيمان».
[صحيح] - [رواه مسلم]

Abu Sa‘īd al-Khudri (may Allah be pleased with him) reported: “I heard the Messenger of Allah (may Allah’s peace and blessings be upon him) say: ‘Whoever of you sees an evil, let him change it with his hand; and if he is not able to do so, then [let him change it] with his tongue; and if he is not able to do so, then with his heart — and that is the weakest level of faith.’”
Sahih/Authentic. - [Muslim]

Explanation

Abu Sa‘īd al-Khudri (may Allah be pleased with him) reported: “I heard the Messenger of Allah (may Allah’s peace and blessings be upon him) say: “Whoever of you sees an evil.” This is an address to all the people, including men and women, children and adults, and all that can be included under the statement: 'whoever of you'. Evil is all that is intrinsically regarded as such. It could be recognized by two tokens: being forbidden under Shariah, or proved as evil by reason. It does not entail a sin except in cases stated by the Lawgiver. Its opposite is what is right, and it is in no way subject to self-inclination or desires. Then the Prophet (may Allah’s peace and blessings be upon him) clarified the degrees of changing what is evil, which varies according to the ability of the person. He started with the first degree, which is to change with one’s hand, and it is for he who has authority or ability to change, provided that he uses wisdom and the change would not result into an equal or greater evil. If he cannot change it by his hand, he should change it by his tongue, which means that he should use a suitable non-provocative way that is not likely to lead to greater evil. If he still cannot change it with his tongue, he should change it by his heart. In other words, if he fears that his words would incur harm upon him, then he should disapprove, dislike, and hate such evil by his heart. This requires him to leave the place where evil is committed if he can. This degree, however, is the weakest form of faith, since this is the least thing one could do in this regard.