He said Santa would have to fly faster than the speed of light to get to every house in one night.
7 seconds sound clip from the The Polar Express movie soundboard.
You can hear this line at 00:02:48 in the Blu-ray version of the movie.
Quote context
[...]
- On Christmas Eve, many years ago, I lay quietly in my bed.
- I did not rustle the sheets. I breathed slowly and silently.
- I was listening for a sound I was afraid I'd never hear: the ringing bells of Santa's sleigh.
- All right. All right, Sarah you had your water. Now let's get you upstairs and into bed.
- He said Santa would have to fly faster than the speed of light to get to every house in one night.
- And to hold everyone's presents his sled would be bigger than an ocean liner.
- Your brother said that? He was just kidding you. He knows there's a Santa.
- He said he wasn't sure. He wasn't sure if Santa was for real.
- Of course Santa's for real. He's as real as Christmas itself.
- But he won't come until you're sound asleep, young lady. Sweet dreams.
[...]