Enders Game

The above quote is not in the book, word for word. The quote added below is the closest thing I can find. Are you sure you're asking about the first book in the series?

"But we don't have him now, Ender. We've scraped together everything mankind could produce, a fleet that makes the one they sent against us last time seem like a bunch of kids playing in a swimming pool. We have some new weapons, too. But it might not be enough, even so. Because in the eighty years since the last war, they've had as much time to prepare as we have. We need the best we can get, and we need them fast. Maybe you're not going to work out for us, and maybe you are. Maybe you'll break down under the pressure, maybe it'll ruin your life, maybe you'll hate me for coming here to your house today. But if there's a chance that because you're with the fleet, mankind might survive and the buggers might leave us alone forever then I'm going to ask you to do it. To come with me."