This is a dangerous time for you, when you will be tempted by the dark side of the Force.
8 seconds sound clip from the Star Wars: Episode V - The Empire Strikes Back movie soundboard.
You can hear this line at 01:23:24 in the Blu-ray version of the movie.
Quote context
[...]
- But Han and Leia will die if I don't.
- Even Yoda cannot see their fate.
- But I can help them. I feel the Force. But you cannot control it.
- This is a dangerous time for you, when you will be tempted by the dark side of the Force.
- Yes! Yes! To Obi-Wan you listen.
- The cave. Remember your failure at the cave.
- But I've learned so much since then.
- Master Yoda, I promise to return and to finish what I've begun. You have my word.
- It is you and your abilities the emperor wants.
[...]