Name That Poem #2

So this one can be considered a poem, but it's actually not a poem. It's still really famous, and it's something I was quoting and discussing with Dawn on my Cali trip.

O, then, I see Queen Mab hath been with you.

Bonus points for anyone who can continue to recite without looking it up online (Dawn is exempt as I know she can recite it). A good answer would include who says this in addition to the author and title of the work.

Do you have a quote you want to try out on folks? Put it in a comment or email me. I love trying to guess poems. It makes me use parts of my brain that have seemingly gone into retirement.

Have fun.