Abu Sa‘id Al-Khudri (may Allah be pleased with him) said,
I heard the Prophet (peace be upon him) saying, ‘Whosoever of you sees an evil action, he must change it with his hand. If he is not able to do so, then he must change it] with his tongue. If he is not able to do so then [he must change it] with his heart and this is the weakest (manifestation) of faith.’ ”
Recorded by Muslim in Kitab Al-Iman (Book on Faith), no, 49/78.