A scene from George RR Martin's "A Clash of Kings".

Jon Snow and Qhorin Halfland, two brothers of the Night's Watch are pursued by relentless enemies through the wilds. One night Qhorin asks Jon if he remembers the word of their vow:

"Do you remember the words of your vow?" asked Qhorin Halfhand across the flickering fire.
"Yes." They were not words a man was like to forget. Once said, they could never be unsaid. They changed your life forever.
"Say them again with me, Jon Snow."
"If you like." Their voices blended like one beneath the rising moon, while Ghost listened and the mountains themselves bore witness.
"Night gathers and now my watch begins. It shall not end until my death. I shall take no wife, hold no lands, father no children. I shall wear no crowns and win no glory. I shall live and die at my post. I am the sword in the darkness. I am the watcher in the walls. I am the fire that burns against the cold, the light that brings the dawn, the horn that wakes the sleepers, the shield that guards the realms of men. I pledge my life and honor to Night's Watch, for this night and all the nights to come."