Lewis Carrol discussion

Okay, this is driving me insane. I made a Goodreads account specifically to find this out. Here is a popular Carroll quote: "She who saves a single soul, saves the universe." This quote is also commonly attributed to the Cheshire Cat. My question is...where?! Don't get me wrong, it's a beautiful sentence, but where in either book does this quote appear???

Answer found thanks to the Lewis Carroll Society of North America. Link to the answer here: https://www.goodreads.com/questions/6...