word to the wise (is enough).and A word to the wise is sufficient.
Prov. You only have to hint something to wise people in order to get them to understand it.; Wise people do not need long explanations. (Often used to signal that you are hinting something.) John's a pleasant man, but I wouldn't trust him with money. A word to the wise, eh? Donna hinted about Lisa's drinking problem to Lisa's fiancé, hoping that a word to the wise would be enough.
McGraw-Hill Dictionary of American Idioms and Phrasal Verbs. © 2002 by The McGraw-Hill Companies, Inc.