Riyad as-Salihin

Abu Sa'id Al-Khudri (May Allah be pleased with him) reported: Messenger of Allah (ﷺ) said, "Whoever amongst you sees an evil, he must change it with his hand; if he is unable to do so, then with his tongue; and if he is unable to do so, then with his heart; and that is the weakest form of Faith".

[Muslim].