THE SECOND= ENTIRETY OF RELIGION

It is reported on the authority of Umar b. al-Khattab that he said:One day, while we were sitting with Rasulallah (s), a man appeared before us. His garments were sparkling white; his hair the darkest black. No signs of travel appeared on him. None of us recognized him. He went to the Prophet (s) and sat in front of him, placing his knees before [the Prophet's] knees.
He also placed his hands upon the Prophet's thighs, saying: 'Muhammad, What is Islam?'
Rasulallah, (s), replied, saying: 'Islam is to testify that there is no deity save Allah and that Muhammad is the messenger of Allah; to establish regular prayer; to give regular alms ("zakat"); to fast Ramadan; and, to visit Allah's House as a pilgrim, if you are able.'
The stranger said, 'You speak the truth.'
Umar said: 'We were amazed that he would ask him [a question], then tell him he was truthful!'
The stranger said: 'Muhammad, what is faith?'
Rasulallah replied, saying: 'Faith is to believe in Allah, His angels, His books, His messengers, the Last Day, and to believe in [the Divine] Power ("Qadar"), its good and its ill.'
The stranger said: 'You speak the truth.' Then, he said: 'What is Ihsan?'
Rasulallah replied, saying: 'Ihsan is to serve Allah as though you see Him, but if you see Him not, then [to serve Him knowing] He sees you.'
The stranger said: 'You speak the truth.' Then, he said: 'Can you inform me about the Hour ("Qiamat")?'
Rasulallah replied, saying: 'The questioned knows no more about it then the questioner.'
The stranger said: 'Then tell me of its signs.'
Rasulallah said: '[Among] its signs are that the slave woman shall give birth to her mistress, and that the poor, naked and barefoot, the herders of sheep, shall compete in raising tall buildings.'
The stranger tarried but a moment before departing.
The Prophet (s) said to me: 'Umar, do you know who was the questioner?'
I replied that Allah and His Messenger knew better.
Rasulallah (s) said: 'This is Jibril. He came to teach you your religion.'
The hadith explains that religion is made up of three elements:
Islam

The Prophet (s) explained that the first category consists of external actions, both conduct and speech. The first external action is to testify that there is no deity save Allah and that Muhammad is the messenger of Allah. The remaining acts, namely, regular prayer, regular alms, fasting Ramadan, and Pilgrimage, all involve conduct that can be described as either involving only the body, e.g., salat and sawm, or involving only property, e.g., paying regular alms, or a composite of the two, e.g., Pilgrimage to Makka al-Mukarrama.
Iman

As for Iman (faith), the Prophet (s) explained it as inner beliefs in the heart, saying that it is belief in Allah, His Angels, His books, His messengers, resurrection after death, and belief in Divine Power, its good and its bad.
Ihsan
The Prophet's explanation of 'ihsan' as worshipping Allah in this manner, namely, drawing forth the feeling of His closeness and that He is with the servant as though he sees Him -this necessarily results in glorification, fear, awe and respect [of Allah]. This condition also leads to sincerity in worship expending all one's ability in improving it, completing it properly and perfecting it. The Prophet, may Allah's blessings and peace be upon him, told several of his companions this advice, namely, to worship Allah as though you see Him, because of the vast benefits such a condition bestows upon the person who attains this level.The second part of the hadith of the Prophet (s) explaining ihsan is that 'if you do not see Him, than He sees you.' Because it is very difficult to attain the level that allows you to worship Allah as though you see Him, the Prophet (s) told us that we may seek to attain that level by means of our knowledge that He certainly sees us.
Signs of The Last Day
When Jibril (s) asked the Prophet (s) about the Last Day, the Prophet (s) disclaimed any knowledge of when it will occur. This is evidence that Allah has kept knowledge of this moment to Himself. Likewise, it shows the importance of saying 'I don't know,' when one is asked about something of which he is ignorant. Far from reducing his stature, admission of ignorance is a sign of piety and fear of Allah.The first sign is that the slave girl gives birth to her master. Some thought of this to refer to children disobeying and treating their parents as slaves. The scholars have understood this to be a reference to the early conquests of Islam and the spread of slaves among the Muslims from the conquered populations, and that the children of these slave women would be their masters, for the child of a master is in the same position, socially, as the master. Thus, the slave woman will give birth to her master.The second sign is that you see the barefoot, the naked, the poor, the herders of sheep, competing in raising tall buildings. The meaning of this is that the undeserving become the leaders of the people. In this expression is criticism of needless luxury and showing off for the purpose of gaining prestige in this life.
p/s: quite a long hadith... :)