Sahih Bukhari Volume 6, Book 61, Hadith Number 532.
Narrated By Aslam : Allah’s Apostle was traveling on one of his journeys, and ‘Umar bin Al-Khattab was traveling along with him at night. ‘Umar asked him about something, but Allah’s Apostle I did not answer him. He asked again, but he did not answer. He asked for the third time!, but he did not answer. On that, ‘Umar said to himself, “May your mother lose you! You have asked Allah’s Apostle three times, but he did not answer at all!” Umar said, “So I made my camel go fast till I was ahead of the people, and I was afraid that something might be! revealed about me. After a little while I heard a call maker calling me, I said, ‘I was afraid that some Qur’anic Verse might be revealed about me.’ So I went to Allah’s Apostle and greeted him. He said, ‘Tonight there has been revealed to me a Surah which is dearer to me than that on which the sun shines (i.e. the world).’ Then he recited: ‘Verily! We have given you (O Muhammad I, a manifest victory.’ ” (Surat al-Fath) No. (48.1).