It was narrated that Abu Hurairah said:
"One day the Prophet (ﷺ) appeared among the people. A man came to him and said: 'O messenger of Allah, what is Iman (faith)?' He said: 'To believe in Allah, His angels, His books, His Messengers and the meeting with, and to believe in the Final Resurrection.' He said: 'O Messenger of Allah, what is Islam?' He said: 'To worship Allah (alone) and not to associate anything with Him; to establish the prescribed prayers, to pay the obligatory Zakat, and to fast Ramadan.' He said: 'O Messenger of Allah, what is Ihsan? He said: 'To worship Allah as if you see Him, for even though you do not see Him, He sees you.' He said: "O Messenger of Allah, when will the Hour be?' He said: 'The one who is being asked about it does not know more than the one who is asking. But I will tell you about its signs. When the slave woman gives birth to her mistress that is one of its signs. When the shepherds compete in constructing tall buildings that is one of its signs. And there are five things which no one knows except Allah.' Then the Messenger of Allah (ﷺ) recited the Verse: "Verily, Allah, with Him (Alone) is the knowledge of the Hour, He sends down the rain, and knows that which is in the wombs. No person knows what he will earn tomorrow, and no person knows in what land he will die. Verily, Allah is All-Knower, All-Aware (of things)."
English reference: Vol. 1, Book 1, Hadith 64
Arabic reference: Book 1, Hadith 67