Your insight serves you well.
2 seconds sound clip from the Star Wars: Episode VI - Return of the Jedi movie soundboard.
You can hear this line at 00:48:05.157 in the Blu-ray version of the movie.
Quote context
[...]
- The other he spoke of is your twin sister.
- To protect you both from the Emperor, you were hidden from your father when you were born.
- The Emperor knew, as I did, if Anakin were to have any offspring, they would be a threat to him.
- That is the reason why your sister remains safely anonymous.
- Your insight serves you well.
- Bury your feelings deep down, Luke. They do you credit, but they could be made to serve the Emperor.
- Well, look at you, a general, huh?
- Someone must have told them about my little manoeuvre at the Battle of Tanaab.
[...]