발 없는 말이 천리 길 간다
Even words without feet travel thousand miles.
Also, can be translated as: Words without feet can go a thousand "ri." ("Ri" is an old form of measurement that equals approximately 0.4 kilometers.)
Same as above. Rumors spread quickly, so be careful of the things you say.
말은 잠깐 사이에 먼 데까지 퍼진다.
Bad news travels fast.