It is narrated from Hazrat Abu Umamah (may Allah be pleased with him) that a man asked the Holy Prophet (peace and blessings be upon him), "What is faith?" The Holy Prophet (peace and blessings be upon him) replied, "When you feel sorrow over your evil deed and happiness over your good deed, then you are a believer." He asked, "What is sin?" The Holy Prophet (peace and blessings be upon him) replied, "When something pricks your heart, then leave it."