What is Islam?

Who can give a better answer than Mohammed, Prophet of Islam, peace be on him, himself?

In a celebrated report, recorded by Bukhari and all the collections of Hadith, it is mentioned as follows:
In the last days of the life of Prophet, one day an unknown visitor came to see him and put to him four questions, viz. What is Iman (Faith), what is Islam (Submission), What is Ihsan (Best Method), and When will come the end of the world? As to the Faith he replied: One should believe in God, in His heavenly agents, in His books (or: prescriptions), in His human messengers(:prophets), in the Dooms day and in the fact that good and evil, all is determined by God. Regarding Submission, he said: Belief in God, daily service of worship prayer, fasting the month of Ramadan, paying the zakat-tax, and pilgrimage of the House of God (in Makkah). The best method, said he: of doing the duty is that you render your duty onto God as if you see Him present; although you do not see Him, yet He sees you. For the last question regarding the moment of the end of the world, which is an elucidation of part of the reply to first question, his answer was: I do not know it better then you, (the day is coming yet none other then God knows it when). When the visitor went away, the Prophet (PBUH) said: It was Gabriel who had come to teach you your religion.