Musnad Abu Ya'la al-Mawsili 2:9

Mus'ab ibn 'Abd Allah ibn Mus'ab al-Zubayri narrated to us, Malik ibn Anas narrated to us, from Zayd ibn Aslam, from his father, that 'Umar ibn al-Khattab was traveling alongside the Messenger of Allah (may Allah bless him and grant him peace) on one of his journeys. He asked him about something, but he did not answer him. Then he asked him, but he did not answer him. Then he asked him, but he did not answer him. 'Umar said: I said to myself, "May your mother be bereaved of you, 'Umar! You asked the Messenger of Allah (may Allah bless him and grant him peace) three times, and each time he did not answer you." So I spurred my camel and went ahead of the people. I had not waited long when I heard a caller calling out. I came, and I said, "I feared that a Quran might have been revealed regarding me." I greeted him, and the Messenger of Allah (may Allah bless him and grant him peace) said: "A Surah was revealed to me tonight that is more beloved to me than that upon which the sun has risen." Then he recited: "Indeed, We have given you a clear conquest, that Allah may forgive for you what preceded of your sin and what will follow."