For those who prefer not to visit yt, the quote "I was there, Gandalf. I was there three thousand years ago" refers to Elrond talking about the time when Isildu

For those who prefer not to visit yt, the quote "I was there, Gandalf. I was there three thousand years ago" refers to Elrond talking about the time when Isildur took the One Ring from Sauron.