Umm... tell that person to not do that any more?

 

Not necessarily the most elegant solution, but as long as you have a contact set up for that person, you can block them each night using the "reject" feature in the contact pop-up menu. To make it quicker, you can set their contact page as a shortcut on one of your home pages, then tap the name on the shortcut to bring up the full contact page, then hit the pop-up menu key and hit reject. Reverse the process each morning.

 

You could create / find a music file which has only silence and specify it as default notification sound inside the settings of that contact. That's the quickest. Or enable blocking mode and specify a custom list of contacts you want to be able to receives texts from.

 

As Gomjaba mentioned, enable blocking mode

settings>my device>blocking mode
switch on
tick disable notifications
set your blocking mode hourse
click allowed contacts
select custom
then add all the contacts who are not insomniac pains in the arse.

 

Use Light Flow to add that person as a new Notification. Then set Quiet Hours in Light Flow, then go back into that persons settings within Light Flow and silence them.

You will still get their messages, but will not be bothered by the sound or notification lights when they send you a text message during your quiet hours.

Or

You can type out a reply to their text message: "This is an automated response. My Quiet Hours are between 9pm and 10am. I did receive your message and will respond to it tomorrow when I am awake."

After typing that out once, I'm sure that person will get the hint and stop texting you during the night. If they don't, then you could set Light Flow to quiet them.