Sahih Muslim Book 4, Hadith Number 1453.

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

Abu Qatada reported that when the Messenger of Allah (may peace be upon him) was in a journey he got down for rest at night, and he used to lie down on his right side, and when he lay down for rest before the dawn, he used to stretch his forearm and place his head over his palm.