Sahih Bukhari, Chapter: Times of the Prayers

Allah's Apostle came out as the sun declined at mid-day and offered the Zuhr prayer. He then stood on the pulpit and spoke about the Hour (Day of Judgment) and said that in it there would be tremendous things. He then said, "Whoever likes to ask me about anything he can do so and I shall reply as long as I am at this place of mine. Most of the people wept and the Prophet said repeatedly, "Ask me." Abdullah bin Hudhafa As-Sahmi stood up and said, "Who is my father?" The Prophet said, "Your father is Hudhafa." The Prophet repeatedly said, "Ask me." Then Umar knelt before him and said, "We are pleased with Allah as our Lord, Islam as our religion, and Muhammad as our Prophet." The Prophet then became quiet and said, "Paradise and Hell-fire were displayed in front of me on this wall just now and I have never seen a better thing (than the former) and a worse thing (than the latter)."