From Sahih muslim Chapter no 1: Faith (Kitab Al Iman)
Hadith No: 6 Narrated/Authority of Abu Huraira
The Messenger of Allah (may peace be upon him) said, “You can ask me about religion.” But the Companions of the Holy Prophet were too respectful to ask anything. Then a man came and sat near him. He asked, “Messenger of Allah, what is al-lslam?” The Holy Prophet replied, “You must only believe in Allah, pray, give to the poor, and fast during Ramadan.” The man said, “You told the truth.” He asked again, “Messenger of Allah, what is al-Iman (faith)?” The Holy Prophet said, “You must believe in Allah, His angels, His Books, His meeting, His Apostles, and you must believe in Resurrection and Divine Decree.” The man said, “You told the truth.” He asked again, “Messenger of Allah, what is al-Ihsan?” The Holy Prophet said, “You must fear Allah as if you can see Him, even though you cannot see Him. He sees you.” The man said, “You told the truth.” The man asked, “When will the hour of Doom come?” The Holy Prophet said, “Only Allah knows. But I can tell you some signs. One sign is when you see a slave woman giving birth to her master. Another sign is when ignorant and foolish people rule the earth. And another sign is when shepherds of black camels build grand buildings. The hour of Doom is one of the five unseen things that only Allah knows.” Then the Holy Prophet recited a verse. Abu Huraira said, “The man stood up and left.” The Messenger of Allah said, “Bring him back to me.” They searched for him, but they couldn’t find him. The Messenger of Allah said, “He was Gabriel and he wanted to teach you about religion when you didn’t ask.”