발 없는 말이 천리 길 간다
foot not-having horse(word)-SUBJ thousand-mile journey goes
A horse with no feet [still] travels a 1000 miles.
This is based on the pun on the fact the word for horse and the word for “word” are the same: 말 [mal]. So a “horse with no feet” is a word, or a rumor. It’s the idea that “rumors fly.” It wasn’t too hard to figure out, except I had to read something to figure out that the pun was going on. I just got the horse with no feet, but I suppose I’d have eventually figured out the pun.