“If you were to offer a thirsty man all wisdom, you would not please him more than if you gave him a drink.”

Source: Dictionary of Burning Words of Brilliant Writers (1895), P. 153.

Attributed to Plato in Confidence : How to Succeed at Being Yourself (1987) by Alan Loy McGinnis, this is probably a paraphrase of a statement which occurs in Letter of Advice to a Young Gentleman Leaving the University Concerning His Behaviour and Conversation in the World (1907) by Richard Lindgard: "Take heed of playing often or deep at Dice and Games of Chance, for that is more chargeable than the seven deadly sins; yet you may allow yourself a certain easie Sum to spend at Play, to gratifie Friends, and pass over the Winter Nights, and that will make you indifferent for the Event. If you would read a man’s Disposition, see him Game; you will then learn more of him in one hour, than in seven Years Conversation, and little Wagers will try him as soon as great Stakes, for then he is off his Guard."
Variants:
You can learn more about a person in an hour of play than in a year of conversation.
Attributed to Plato in Food Is the Frosting-Company Is the Cake (2007) by Maggie Marshall
You learn more about a person in an hour of play than in a year of conversation.
Attributed to Plato by former Alaska Gov. Sarah Palin, as quoted in "Aspiring philosopher Palin quotes 'Plato'" (9 July 2009) http://thinkprogress.org/2009/07/09/palin-plato/
Misattributed

Source: Book of Malachi, Chapter 1, Verse 8, Lines 3-8, (NKJV)

Source: Pride and Prejudice

Melincourt, chapter XVI.

Letter IV : Heloise to Abelard
Letters of Abelard and Heloise
Context: I own, to my confusion, I fear more the offending of man than the provoking of God, and study less to please him than you. Yes, it was your command only, and not a sincere vocation, as is imagined, that shut me up in these cloisters. I fought to give you ease, and not to sanctify myself. How unhappy am I? I tear myself from all that pleases me? I bury myself here alive, I exercise my self in the most rigid fastings; and such severities as cruel laws impose on us; I feed myself with tears and sorrows, and, notwithstanding this, I deserve nothing for all the hardships I suffer. My false piety has long deceived you as well as others. You have thought me easy, and yet I was more disturbed than ever. You persuaded yourself I was wholly taken up with my duty, yet I had no business but love. Under this mistake you desire my prayers; alas! I must expect yours. Do not presume upon my virtue and my care. I am wavering, and you must fix me by your advice. I am yet feeble, you must sustain and guide me by your counsel.

Riyadh-as-Saliheen by Imam Al-Nawawi, volume 3, hadith number 436
Sunni Hadith

The testament of Rabbi Israel Baal Shem Tov, translated by (Brooklyn: Kehot Publication Society, 1998), ch. 12.