The Fellowship of the Ring
"You were beginning to fade," answered Gandalf. "The wound was overcoming you at last. A few more hours and you would have been beyond our aid. But you have some strength in you, my dear Hobbit! As you showed in the Barrow-downs. That was touch and go: perhaps the most dangerous moment of all. I wish you could have held out at Weathertop." (2.1.10)
"Slow should you be to wind that horn again, Boromir," said Elrond, "until you stand once more on the borders of your land, and dire need is on you."
"Maybe," said Boromir. "But always I have let my horn cry at setting forth, and though thereafter we may walk in the shadows, I will not go forth as a thief in the night" (2.3.66-7).
Gimli took his arm and helped him down to a seat on the step. "What happened away up there at the door?" he asked. "Did you meet the beater of the drums?"
"I do not know," answered Gandalf. "But I found myself suddenly faced by something that I had not met before. I could think of nothing to do but to try and put a shutting-spell on the door. I know many; but to do things of that ind rightly requires time, and even then the door could be broken by strength. […]
"What it was I cannot guess, but I have never felt such a challenge. The counter-spell was terrible. It nearly broke me!" (2.5.53-4, 56)