I found it! 😄 It's not in Chapter 3, it's in Chapter 2, "The Shadow of the Past" when Frodo and Gandalf were talking about the Ring. 😄
"'Ah!’ said Gandalf. ‘That is a very long story. The beginnings lie back in the Black Years, which only the lore-masters now remember. If I were to tell you all that tale, we should still be sitting here when Spring had passed into Winter.
‘But last night I told you of Sauron the Great, the Dark Lord. The rumours that you have heard are true: he has indeed arisen again and left his hold in Mirkwood and returned to his ancient fastness in the Dark Tower of Mordor. That name even you hobbits have heard of, like a shadow on the borders of old stories. Always after a defeat and a respite, the Shadow takes another shape and grows again.’
‘I wish it need not have happened in my time,’ said Frodo.
‘So do I,’ said Gandalf, ‘and so do all who live to see such times. But that is not for them to decide. All we have to decide is what to do with the time that is given to us. And already, Frodo, our time is beginning to look black. The Enemy is fast becoming very strong. His plans are far from ripe, I think, but they are ripening. We shall be hard put to it. We should be very hard put to it, even if it were not for this dreadful chance.
😄