Is there a quote in Alice Wonderland saying something is so?

You're likely thinking of the famous line from *Alice's Adventures in Wonderland*:

"Curiouser and curiouser!"

While this line doesn't explicitly state something "is so," it captures the sense of wonder and absurdity that permeates the story. Alice's repeated exclamation of "curiouser and curiouser" emphasizes the strange and unbelievable events happening around her, making it a suitable answer to your question.

Let me know if you'd like to explore other quotes from Alice in Wonderland!