Sayyiduna Abu Sa'id al-Khudri (may Allah be pleased with him) said that the Messenger of Allah (peace and blessings be upon him) said: "Whoever sees an evil should stop it with his hand; if he lacks the strength to stop it with his hand, then he should forbid it with his tongue; and if he lacks the strength to forbid it even with his tongue, then he should reject it with his heart, and that is the weakest degree of faith."
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الصداق / 14548