THINKING MUSLIM : IMAN, ISLAM & IHSAN
The following hadith is rather lengthy but an important one. Briefly, it talks about the time when the angel Jibril visited the Prophet (pbuh), coming dressed as a man unknown, and asked him what IMAN is, what ISLAM is, and what IHSAN is. I left out the last third of the hadith, in which the Prophet relates the signs of the world approaching the Hour.
Abu Huraira reported: One day the Messenger of Allah (may peace be upon him) appeared before the public that a man came to him and said: Prophet of Allah, (tell me) what is Iman. Upon this he (the Holy Prophet) replied: That you affirm your faith in Allah, His angels, His Books, His meeting, His Messengers and that you affirm your faith in the Resurrection hereafter.
He (again) said: Messenger of Allah, (tell me) what does al-Islam signify. He (the Holy Prophet) replied: Al-Islam signifies that you worship Allah and do not associate anything with Him and you establish obligatory prayer and you pay the obligatory poor-rate (Zakat) and you observe the fast of Ramadan.
He (the inquirer) again said: Messenger of Allah, what does al-Ihsan imply? He (the Holy Prophet) replied: That you worship Allah as if you are seeing Him, and in case you fail to see Him, then observe prayer (with this idea in your mind) that (at least) He is seeing you.
Book 001, Number 0004, read Sahih Muslim.