Sahih Muslim Book 1 – Hadith 7

It is narrated on the authority of Abu Huraira that the Messenger of Allah (ﷺ) said:

Ask me (about religious matters), but they (the Companions) were in awe of asking him. Then came a man, and sat near his knees and said: O Messenger of Allah, what is al-Islam? So he (the Holy Prophet) replied: [That] you do not associate anything with Allah, and establish the prayer, pay the alms (Zakat) and fast Ramadan. He said: You (have) told the truth. He said: Messenger of Allah, what is al-Iman (Faith)? He said: That you affirm your faith in Allah, His angels, His Books, His meeting, His Apostles, and that you believe in Resurrection and that you believe in Qadr (Divine Decree) in all its entirety. He (the inquirer) said: You have told the truth. He said: Messenger of Allah, what is al-Ihsan? Upon this he said: that you fear Allah as if you are seeing Him, and though you see Him not, verily He is seeing you. He (the inquirer) said: You (have) told the truth. He (the inquirer) said: When will the Hour (of Doom) occur? He said: The one who is being asked about it is no better informed than the inquirer and I will narrate some of its signs to you. When you see a [slave] woman giving birth to her master - then that is [one] of its signs. And when you see barefooted, naked, deaf and dumb (ignorant and foolish persons) as the rulers of the earth - then that is [one] of its signs. And when you see the shepherds of black (camels) exult in buildings - then that is [one] of its signs. The (Hour) is one of the five things of the unseen. No one knows them except Allah. Then (the Holy Prophet) recited (the folowing verse):" Verily Allah! with Him alone is the knowledge of the Hour and He it is Who sends down the rain and knows that which is in the wombs. And no soul knows what it shall earn on the morrow and a soul knows not in what land it shall die. Verily Allah is Knowing, Aware."

He (Abu Huraira) said: Then the person stood up (and made his way). Then the Messenger of Allah (ﷺ) said: Bring him back to me. He was searched for, but they could not find him. The Messenger of Allah (ﷺ) thereupon said: He was Gabriel and he wanted to teach you when you did not ask. (Sahih Muslim Book 1 – Hadith 7)