Who said "Pain is just weakness leaving the body."?

This quote is attributed to Nelson Muntz.

Pain is just weakness leaving the body. - Nelson Muntz

"Pain is just weakness leaving the body."

Nelson Muntz Perseverance

"Ha-ha!"

"Your tears of unfathomable sadness!"

"I'm gonna enjoy this, Bart. I'm gonna enjoy this a lot."

"Eat my shorts, Simpson!"

"Perseverance is the key to success."

"Don't give up on what you believe in."

"I've been through worse."

"You learn to live with the pain."