The Practice of religion of Islam involves the believer in the three great categories islam (submission to the revealed law), iman (faith in the shahada) and ihsan (virtue or sincerity). The following Hadith is reported by the Caliph 'Hazrat Umar':

One day when we were with the Messenger of God there came unto us a man whose clothes were of  exceeding whiteness and whose hair was of exceeding blackness, nor were there any signs of travel upon him, although non of us had seen him before. He sat down knee unto knee opposite the Prophet, upon whose thighs he placed the palm of his hands, saying : ' O Muhammed, tell me what is the surrender unto God (al-islam).' the Prophet answered: ' The surrender is that thou shouldst perform the prayer, bestow the alms, fast Ramadan, and make, if though canst, the piligrimage of the Holy House.' He said: ' thou hast spoken truly' and we were amazed that having questioned him he should corroborate him. Then he said : 'Tell me what is fath (iman), and the Prophet answered: 'It is that though should believe in God and His Angels and His Books and His Apostles and the and the Last Day, and thou shouldst believe that no good or evil cometh but by His Providence.' 'Thou hast spoken truly', he said, and then : ' Tell me what is excellence (ihsaan).' The Prophet answered : 'It is that thou shouldst worship God as if thou sawest Him, for if thou seest Him not, verily He seeth thee'... Then the stranger went away, and I stayed there long after he had gone, until the Prophet said to me: 'o ' Umar , knowest thou the questioner, who he was?' I said: 'God and His Prophet know best, but I know  not at all..' It was Gabriel' said the Prophet. 'He came to teach you your religion.