Hazrath Abu Huraira Rz. narrated:
One day while the Prophet (May Allah bless him and give him peace) was sitting in the company of some people, (The angel) Hazrath Gabriel Alaihissalam came and asked, "What is faith?" Allah's Apostle (May Allah bless him and give him peace) replied, 'Faith is to believe in Allah, His angels, (the) meeting with Him, His Apostles, and to believe in Resurrection." Then he further asked, "What is Islam?" Allah's Apostle (May Allah bless him and give him peace) replied, "To worship Allah Alone and none else, to offer prayers perfectly to pay the compulsory charity (Zakath) and to observe fasts during the month of ramadan." Then he further asked, "What is Ihsan (perfection)?" Allah's Apostle,(May Allah bless him and give him peace) replied, "To worship Allah as if you see Him, and if you cannot achieve this state of devotion then you must consider that He is looking at you." Then he further asked, "When will the Hour be established?" Allah's Apostle (May Allah bless him and give him peace) replied, "The answerer has no better knowledge than the questioner. But I will inform you about its portents. 1. When a slave (lady) gives birth to her master. 2. When the shepherds of black camels start boasting and competing with others in the construction of higher buildings. And the Hour is one of five things which nobody knows except Allah. The Prophet (May Allah bless him and give him peace) then recited: "Verily, with Allah (Alone) is the knowledge of the Hour--." (31. 34) Then that man (Hazrath Gabriel Alaihissalam) left and the Prophet (May Allah bless him and give him peace) asked his companions to call him back, but they could not see him. Then the Prophet (May Allah bless him and give him peace) said, "That was Gabriel who came to teach the people their religion." Hazrath Abu 'Abdullah Rz. said: He (the Prophet,May Allah bless him and give him peace ) considered all that as a part of faith. - (Sahih Bukhari).