Who said "I've learned that true strength comes from within."?

This quote is attributed to Snoopy.

I've learned that true strength comes from within. - Snoopy

"I've learned that true strength comes from within."

Snoopy Strength

"I think I'm dying. Send for a doctor immediately!"

"Rats! Another day, another disappointment."

"Sometimes I lie awake at night and ask, 'Is life a multiple choice test or an essay?' Then a dog barks and I realize it doesn't matter."

"I love mankind. It's people I can't stand."

"Strength comes from within."

"A woman should be proud of who she is."

"A strong woman can overcome anything."

"The only thing I'm good at is killing."