Narrated by Abu Huraira (Radhiallaho anho):

One day while the Prophet was sitting in the company of some people, (The angel) Gabriel came and asked, "What is faith?" Allah's Messenger (sallallaahu 'alaihi wasallam) replied, "Faith is to believe in Allah, His angels, (the) meeting with Him, His Apostles, and to believe in Resurrection." Then he further asked, "What is Islam?" Allah's Messenger (sallallaahu 'alaihi wasallam) replied, "To worship Allah Alone and none else, to offer prayers perfectly to pay the compulsory charity (Zakat) and to observe fasts during the month of Ramadan." Then he further asked, "What is Ihsan (perfection)?" Allah's Messenger (sallallaahu 'alaihi wasallam) replied, "To worship Allah as if you see Him, and if you cannot achieve this state of devotion then you must consider that He is looking at you." Then he further asked, "When will the Hour be established?" Allah's Messenger (sallallaahu 'alaihi wasallam) replied, "The answerer has no better knowledge than the questioner. But I will inform you about its portents.

• When a slave (lady) gives birth to her master.

• When the shepherds of black camels start boasting and competing with others in the construction of higher buildings. And the Hour is one of five things which nobody knows except Allah.

The Prophet then recited: "Verily, with Allah (Alone) is the knowledge of the Hour--." (Sura Luqman:Ver.34) Then that man (Gabriel) left and the Prophet (sallallaahu 'alaihi wasallam) asked his companions to call him back, but they could not see him. Then the Prophet (sallallaahu 'alaihi wasallam) said, "That was Gabriel who came to teach the people their religion." Abu 'Abdullah said: He (the Prophet (sallallaahu 'alaihi wasallam)) considered all that as a part of faith.

Bukhari Vol. 1 : No. 47 Dual Eclipses and Ramadan - Siraj Desai
Imaam Mahdi (RA) in 2004? - Al-Haadi
Major Signs and Protection From Dajjal - Al-Jumuah
Signs of Qiyamah - by Mohammad Ali bin Zubair Ali and Mufti A.H. Elias
    Forward
    Importance
    Minor Signs
    Jesus (Isa) A.S. in Islam, and his Second Coming
    Imam Mahdi (Descendent of Prophet Muhammad PBUH)
    Who is the evil Dajjal (the "anti-Christ")?
    Who are the Ya'jooj and Ma'jooj?
Surah Al-Qiyámah (the Resurrection) - Qur'an 75