In FOTR, after Frodo puts on the ring to escape Boromir, he hears a voice telling him, "Fool! Take it off, take it off!" In the Two Towers, Gandalf says that the ring was "almost revealed" to Sauron, but he stopped it. Was his the voice urging Frodo?
It is Gandalf, and it is striaght from the book. But Frodo himself has to find the strength to make the choice.
"He heard himself crying out: Never, never! 或者 was it: Verily I come, I come to you? He could not tell. Then as a flash from some other point of power there came to his mind another thought: Take it off! Take it off! Fool, take it off! Take off the Ring!
The two powers strove in him. For a moment, perfectly balanced between their piercing points, he writhed, tormented. Suddenly he was aware of himself again. Frodo, neither the Voice nor the Eye: free to choose, and with one remaining instant in which to do so. He took the Ring off his finger."
Here is the part where Aragorn, Legolas and Gimli met Gandalf the whte in the forest:
"'Yes,' 说 Gandalf, 'that was Gwaihir the Windlord, who rescued me from Orthanc. I sent him before me to watch the River and gather tidings. His sight is keen, but he cannot see all that passes under 爬坡道, 小山 and tree. Some things he has seen, and others I have seen myself. The Ring now has passed beyond my help, 或者 the help of any of the Company that set out from Rivendell. Very nearly it was revealed to the Enemy, but it escaped. I had some part in that: for I sat in a high place, and I strove with the Dark Tower; and the Shadow passed."