Grief, it's a running gag.
2 seconds sound clip from the The Muppet Movie (1979) movie soundboard.
You can hear this line at 00:14:13.378 in the Blu-ray version of the movie.
Quote context
[...]
- Hey, wacka, wacka. Ah, wacka, wacka, wacka.
- Here I am, Fozzie Bear, to tell you jokes both old and rare. Wacka, wacka, wacka.
- Ha, ha. Let's start things off with a bang.
- Thank you, sir. Wacka, wacka, wacka, wacka, wacka.
- Maybe he should try Hare Krishna.
- There was this sailor who was so fat...
- Uh... He was so fat that everybody liked him and there was nothing funny about him at all.
- Oh, wait, please. Oh, please. Please wait. I'm trying so hard. Please don't do that.
- I'm a professional. I've had three performances.
[...]