Narrated by Umar ibn al-Khattab: One day while we were sitting with the Messenger of Allah, peace and blessings be upon him, there appeared before us a man dressed in extremely white clothes and with very black hair. No traces of journeying were visible on him, and none of us knew him. He sat down close by the Prophet knee to knee, and rested his hands on his thighs and said, “Oh Muhammad! Inform me about Islam" The Messenger of Allah, peace be upon him, said "Islam is that you should testify that there is no deity save Allah and that Muhammad is His Messenger, that you should uphold prayer, pay the zakah (charity), fast during Ramadan, and perform pilgrimage to the House (the Ka'bah in Makkah), if you can find the means." The man said "You have spoken truly." We were astonished at his thus questioning him and telling him that he was right, but he went on to say, "Inform me about faith" The Messenger of Allah answered, "It is that you believe in Allah and His angels and His Books and His Messengers and in the Last Day, and in divine decree, both the good and the evil thereof." He said, "You have spoken truly." Then he said, "Inform me about Goodness" The Messenger of Allah answered, "It is that you should serve Allah as though you could see Him, for though you cannot see Him yet He sees you." He said, "Inform me about the Hour." The Messenger of Allah said "About that the one questioned knows no more than the questioner." Then man left. I waited a while, and then he (the Messenger of Allah) said, "Oh 'Umar, do you know who that questioner was?" "Allah and His Messenger know better." I replied. He said, "That was the angel Jibril (Gabriel). He came to teach you your religion."