This doesn’t exactly count as legal research, but I periodically get asked for to confirm that a given person was the source of a quote. Most of the time, it’s fairly easy to track down, but in other cases, I end up using https://quoteinvestigator.com. It’s a wonderful resource for those situations where the quote you’ve been given might have been said by a number of different people and not in those precise words. Note that you will need to scroll down a little bit before you find the search box on the left hand side.
A Research Tip