We don't need clues, Robin. We know our man is The Joker. What we need is evidence.

7 seconds sound clip from Batman (1966) - The Joker Goes to School (S1E15) TV Series.

You can hear this line at 00:19:00 in the Blu-ray version of the movie.

Quote context

[...]

- X plus Y times X plus Y... Holy alphabet, what is it?

- If you'll excuse me, Master Robin. The solution is X squared plus 2XY plus Y squared.

- Gee, sure! Why didn't I know that? And with nationwide pre-college exams coming up in just three days.

- Good to have you home.

- What'd you find out, Batman?

- Nothing. Holy vacuum, not a single clue?

- We don't need clues, Robin. We know our man is The Joker. What we need is evidence.

- I went over that looted lounge with a fine toothed comb. I didn't even find a single hair to analyze.

- Gosh. And school morale in a tailspin.

- Come a month from now, there'll be dropouts by the bushel.

- If he waits that long.

- I didn't want to cause panic at the student meeting, but I think The Joker has some other dirty plan afoot as well.

[...]