What is Islam? Who can give a better answer than Muhammad, 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 the Prophet, one day an unknown visitor came to see him and put to him four questions: What is iman (faith), what is Islam (submission), what is ihsan (best method), and when will come the end of the world? As to Faith, he replied: one should believe in God, in His heavenly agents, in His books (or: prescriptions), in His human messengers (or: 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 services of worship-prayer, fasting in the month of Ramadan, paying the zakat-tax, and pilgrimage to the House of God (in Mecca). The Best method, said he, of doing the duty is that you render your duty unto 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 the first question, his answer was: I do not know it better than you, (the day is coming yet none other than God knows when). When the visitor went away, the Prophet said: It was Gabriel who had come to teach you your religion.