LEELA: Never mind, Doctor, I’ve found the answer.

DOCTOR: You have?

LEELA: Knife them in the neck!

Doctor Who (1963-1989) British science fiction television series, original run (BBC)

15×02 “The Invisible Enemy,” Part 4 (1977-10-22) [w. Bob Baker, Dave Martin]
    (Source)

(Source (Video), dialog verified). Sometimes paraphrased: "Don't worry, Doctor. I found the answer: knife them in the neck!"