Don’t if you intend to publish.
Basically unless your quote is under the public domain or you have permission, you are taking someone else’s intellectual property without permission and using it for financial gain. At best, that’s ethically not ideal. At worst, you’ll get a takedown notice/legal action/COG is within their rights to refuse to publish on copyright violation grounds.
The reason for this is because quotes from Socrates are under public domain. There is a reason why you get a tonne of mugs and stickers about with old quotes on them. It’s because legally they CAN be used.
I’ve brought this up multiple times on the forum. Recommend this for reading: Quotes in games, how long can they be? What to remember? - #10 by Jacic