Sahih Muslim Book 4, Hadith Number 1452.

Chapter : The excellence of Qunut in all the prayers when any calamity befalls the Muslims.

‘Imran b. Husain reported: We were with the Messenger of Allah (may peace be upon him) in a journey and we travelled throughout the night till at the end, just before dawn, we lay down (for rest), and nothing is sweeter for a traveller than this and none awakened us but the heat of the sun, and the rest of the Hadith is the same (as mentioned above) except this ahadith: “When ‘Umar b. Khattab woke up, he saw what had happened to the people. And he was a man having a big belly and strongly built; he recited takbir in a loud voice till the Messenger of Allah (may peace be upon him) woke up by the loudness of his voice in takbir. When the Messenger of Allah (may peace be upon him) got up, the people told him what had happened. Upon this the Messenger of Allah (may peace be upon him) said: There is no harm; you better proceed further,” and (the rest of the Hadith) was narrated.