Here's the answer:
“tais-toi s'il te plaît”
Watch a real native speaker say it:
Here's how it sounds in a textbook:
You could also say:
- tais toi s'il te plait
- tais-toi s'il te plait
Fun fact: the hundreds of thousands of people learning French with Memrise get this phrase correct 95.25% of the time!