" ...In this connection was revealed one of the many verse which refer to the heart as the faculty by which man has sight of supernatural realities. The eye of the heart, though closed in fallen man, is able to take in a glimmering of light and this is faith. But an evil way of living causes a covering like rust to accumulate over the heart so that it cannot sense the Divine origin of God’s message... "

― , Muhammad: His Life Based on the Earliest Sources